CSMLS MLT Certification — Questions and Answers

Question 1: In flow cytometry, CD4+ and CD8+ T cell counts are used to monitor:

Rheumatoid arthritis activity
HIV disease progression and immune status (Correct answer)
Hepatitis C viral load
Allergic response severity

Correct answer: HIV disease progression and immune status

CD4+ T helper cell counts are used to monitor HIV disease progression and guide antiretroviral therapy decisions.

Question 2: Which of the following situations will cause mast cells to turn blue during metachromatic staining?

Increased pH of toluidine blue
Decreased pH of toluidine blue (Correct answer)
Tissue improperly fixed
Alcohol used in dehydration

Correct answer: Decreased pH of toluidine blue

Explanation: Mast cells turn blue during metachromatic staining when the pH of toluidine blue decreases. Metachromatic staining relies on the differential affinity of dyes for specific cellular components. Decreasing the pH of toluidine blue enhances its affinity for mast cell granules, causing them to turn blue.

Question 3: An alpha-hemolytic, catalase-negative, Gram-positive coccus is isolated from a sputum culture. The colonies are mucoid and demonstrate a zone of inhibition of 16 mm around a 5 µg optochin disk. What is the most likely identification of this organism?

Streptococcus pneumoniae (Correct answer)
Streptococcus pyogenes
Enterococcus faecalis
Streptococcus agalactiae

Correct answer: Streptococcus pneumoniae

*Streptococcus pneumoniae* is characteristically alpha-hemolytic and is susceptible to optochin, typically showing a zone of inhibition of 14 mm or greater around a 6mm, 5 µg disk. Its presence in a sputum culture, along with the mucoid colony appearance (suggesting a capsule), strongly indicates this identification. *S. agalactiae* and *S. pyogenes* are beta-hemolytic, and *Enterococcus faecalis* is typically non-hemolytic or alpha-hemolytic but is optochin-resistant.

Question 4: A technologist performs a CAMP test to identify a beta-hemolytic Streptococcus isolated from a neonatal blood culture. An arrowhead-shaped zone of enhanced hemolysis is observed where the isolate meets the streak of Staphylococcus aureus. This result is indicative of which organism?

Streptococcus bovis (Group D)
Streptococcus pyogenes (Group A)
Staphylococcus aureus
Streptococcus agalactiae (Group B) (Correct answer)

Correct answer: Streptococcus agalactiae (Group B)

The CAMP test is a classic method used for the presumptive identification of *Streptococcus agalactiae* (Group B Streptococcus). This organism produces a protein called CAMP factor that acts synergistically with the beta-hemolysin produced by *Staphylococcus aureus*, resulting in an arrowhead-shaped zone of enhanced hemolysis. *S. agalactiae* is a significant cause of neonatal sepsis and meningitis.

Question 5: Northern blotting is used to:

Identify specific proteins by antibody probing
Determine the chromosomal location of a gene
Detect and quantify specific mRNA transcripts in a sample (Correct answer)
Detect specific DNA sequences in genomic samples

Correct answer: Detect and quantify specific mRNA transcripts in a sample

Northern blotting separates RNA by electrophoresis, transfers it to a membrane, and hybridizes it with a labeled probe to detect and estimate the size and abundance of specific mRNA molecules.

Question 6: Which cell type is the primary producer of antibodies?

Plasma cell (Correct answer)
T lymphocyte
Macrophage
Natural killer cell

Correct answer: Plasma cell

Plasma cells are terminally differentiated B lymphocytes that are the primary producers of antibodies (immunoglobulins).

Question 7: What is the proper order for the removal of personal protective equipment?

Gown, mask, gloves, eye protection
Gloves, mask, eye protection, gown
Gown, gloves, eye protection, mask
Gloves, gown, eye protection, mask (Correct answer)

Correct answer: Gloves, gown, eye protection, mask

Explanation: The proper order for the removal of personal protective equipment (PPE) is crucial to minimize the risk of contamination and ensure safety. Starting with removing gloves first, followed by the gown, eye protection, and finally the mask, helps prevent potential exposure to hazardous materials and pathogens.

Question 8: The presence of Auer rods within blasts on a peripheral blood smear is most strongly associated with which of the following conditions?

Acute Myeloid Leukemia (AML) (Correct answer)
Chronic Lymphocytic Leukemia (CLL)
Chronic Myeloid Leukemia (CML)
Acute Lymphoblastic Leukemia (ALL)

Correct answer: Acute Myeloid Leukemia (AML)

Auer rods are needle-like, azurophilic cytoplasmic inclusions that are pathognomonic for myeloid blasts. They are formed from the abnormal fusion of primary granules. While not present in all cases of Acute Myeloid Leukemia (AML), their presence confirms a myeloid lineage and is a key morphological feature for diagnosing AML, particularly the acute promyelocytic leukemia (APL) subtype.

Question 9: Which of the following procedures should be used when disposing of a used microtome knife blade?

Have a designated person to collect all blades
Use forceps to handle the blade and place it in sharps (Correct answer)
Grasp the blade in the centre with your fingers and place it in sharps
Wear gloves to handle the blade and place in a biohazard bag

Correct answer: Use forceps to handle the blade and place it in sharps

Explanation: Proper handling and disposal of used microtome knife blades are essential to prevent injuries and ensure safety in the laboratory. Using forceps to handle the blade minimizes the risk of accidental cuts or punctures. Placing the used blade in a sharps container ensures safe disposal and compliance with biohazards waste management protocols.

Question 10: In cerebrospinal fluid (CSF) analysis, xanthochromia (yellow discoloration) indicates:

Bacterial meningitis
Normal finding
Viral encephalitis
Previous subarachnoid hemorrhage (Correct answer)

Correct answer: Previous subarachnoid hemorrhage

Xanthochromia results from oxyhemoglobin and bilirubin released by lysed red blood cells after subarachnoid hemorrhage.

Question 11: According to WHMIS 2015, what does a pictogram showing a flame over a circle represent?

Compressed gas
Oxidizing hazard (Correct answer)
Flammable material
Explosive material

Correct answer: Oxidizing hazard

The flame over circle pictogram indicates an oxidizing substance that can intensify fire or cause combustion by providing oxygen, a critical hazard in laboratories storing multiple chemical types.

Question 12: The presence of nitrite on a urine dipstick suggests:

Glomerulonephritis
Renal calculi
Bacterial urinary tract infection (Correct answer)
Diabetic nephropathy

Correct answer: Bacterial urinary tract infection

Nitrite is produced when certain bacteria (e.g., Gram-negative rods) reduce dietary nitrate, indicating a likely bacterial UTI.

Question 13: A patient's ABO typing results are as follows: Anti-A: 4+, Anti-B: 4+, A1 Cells: 2+, B Cells: 2+. All tubes, including the autocontrol, show agglutination at the immediate spin phase. Microscopic examination reveals rouleaux. What is the best technique to resolve this discrepancy?

Perform saline replacement on the reverse grouping tubes. (Correct answer)
Perform a Direct Antiglobulin Test (DAT).
Adsorb the cold autoantibody from the plasma.
Test the patient's cells with anti-A1 lectin.

Correct answer: Perform saline replacement on the reverse grouping tubes.

This is a classic presentation of a Group 3 discrepancy caused by rouleaux formation, often due to abnormal plasma proteins (e.g., in multiple myeloma). Rouleaux causes non-specific aggregation of red cells. The saline replacement technique resolves this by dispersing the rouleaux; the technologist removes the patient's plasma and replaces it with saline. True agglutination will remain, while rouleaux will disperse. [2, 5, 9]

Question 14: Multiplex PCR panels used in clinical microbiology laboratories are designed to:

Determine minimum inhibitory concentrations for antibiotics
Measure the host immune response to infection
Genotype a single organism at all its resistance loci
Simultaneously detect multiple pathogens in a single reaction (Correct answer)

Correct answer: Simultaneously detect multiple pathogens in a single reaction

Multiplex PCR includes multiple primer sets targeting different pathogens, allowing simultaneous detection of panels such as respiratory viruses or gastrointestinal pathogens from a single patient specimen.

Question 15: A medical laboratory technologist spills approximately 10 mL of 1 Molar hydrochloric acid on a countertop. Which of the following is the most appropriate initial action?

Wipe the spill immediately with absorbent paper towels.
Consult the Safety Data Sheet (SDS) before taking any action.
Cover and neutralize the spill with sodium bicarbonate powder. (Correct answer)
Evacuate the laboratory and call the emergency response team.

Correct answer: Cover and neutralize the spill with sodium bicarbonate powder.

For a small, manageable acid spill, the primary immediate action is to neutralize it. Sodium bicarbonate is a weak base commonly used for this purpose, which safely neutralizes the acid before cleanup. [2, 4] Wiping with paper towels alone could spread the corrosive chemical and risk skin contact. Evacuation is unnecessary for a minor spill, and while consulting the SDS is important for understanding all hazards, the immediate neutralization of a known common acid is the standard first step. [20]

Question 16: A discrepancy is observed where the forward grouping suggests Group O (No agglutination with Anti-A or Anti-B), but the reverse grouping suggests Group A (agglutination with B cells only). The patient has a history of leukemia. What is the most likely cause of this discrepancy?

Chimerism from a recent stem cell transplant.
Weakened A antigen expression due to malignancy. (Correct answer)
Transfusion of non-group specific plasma.
Presence of a potent cold autoantibody.

Correct answer: Weakened A antigen expression due to malignancy.

This is a Group 2 discrepancy, characterized by weak or missing antigens in the forward grouping. [4] Certain diseases, particularly hematologic malignancies like leukemia, can suppress the expression of ABO antigens on red blood cells, leading to weaker-than-expected or negative reactions in the forward type. [3, 4] The reverse grouping, which reflects the patient's true ABO antibodies, remains as expected for their actual blood group.

Question 17: A patient's blood gas results on room air are: pH 7.25, pCO2 60 mmHg, HCO3- 24 mmol/L. Which of the following conditions is most consistent with these findings?

Metabolic alkalosis
Metabolic acidosis
Respiratory alkalosis
Respiratory acidosis (Correct answer)

Correct answer: Respiratory acidosis

The pH is low (<7.35), indicating acidosis. The pCO2 is high (>45 mmHg), indicating a respiratory cause. The HCO3- is within the normal range (22-28 mmol/L), suggesting the acidosis is not of metabolic origin and is uncompensated. Therefore, the results are consistent with respiratory acidosis.

Question 18: Red blood cell casts in urine sediment are pathognomonic of:

Nephrotic syndrome
Glomerulonephritis (Correct answer)
Urinary tract infection
Renal calculi

Correct answer: Glomerulonephritis

RBC casts form when erythrocytes enter the tubular lumen through damaged glomeruli and are diagnostic of glomerulonephritis.

Question 19: What is the primary purpose of proficiency testing (PT) in a clinical laboratory?

To determine how many samples can be processed per hour
To calibrate instruments to manufacturer specifications
To assess laboratory performance by comparing results with other laboratories analyzing the same samples (Correct answer)
To train new staff on instrument operation

Correct answer: To assess laboratory performance by comparing results with other laboratories analyzing the same samples

Proficiency testing involves analyzing unknown samples provided by an external organization and comparing results with peer laboratories, serving as an external check on laboratory accuracy and competency.

Question 20: Which of the following pieces of equipment provides protection from aerosols while aliquoting specimens?

Biological Safety Cabinet (Correct answer)
Canopy Hood
Splash Screen
Fume Hood

Correct answer: Biological Safety Cabinet

Explanation: A Biological Safety Cabinet (BSC) provides protection from aerosols while aliquoting specimens. BSCs are designed to provide a sterile environment and protect laboratory personnel, the environment, and the sample being handled from potential contamination by aerosols or hazardous particles.

Question 21: A histotechnologist is cutting paraffin sections of a kidney block and observes regularly spaced parallel lines, or 'chatter', across the tissue. What is the most likely cause of this microtomy artifact?

The block was too warm during sectioning.
The clearance angle of the knife was too small.
The paraffin wax was contaminated with clearing agent.
The block or knife was not securely clamped in the microtome. (Correct answer)

Correct answer: The block or knife was not securely clamped in the microtome.

Chatter is a vibration artifact characterized by thick and thin zones in the section. It is most frequently caused by a lack of rigidity in the system, such as a loosely clamped block or knife holder, which allows for vibration during the cutting stroke. [2] Other less common causes can include cutting too fast or a block that is overly hard.

Question 22: Analytical sensitivity in a molecular diagnostic test refers to:

The proportion of non-infected patients who test negative
The lowest concentration of target nucleic acid reliably detected above background (Correct answer)
The ability of the assay to distinguish the target from closely related organisms
The proportion of infected patients who test positive

Correct answer: The lowest concentration of target nucleic acid reliably detected above background

Analytical sensitivity, often expressed as the limit of detection (LoD), is the smallest quantity of target that can be consistently detected; it is distinct from clinical sensitivity, which describes performance in the patient population.

Question 23: A bronchial washing specimen for routine bacterial, fungal and acid-fast culture was received. The sample volume is insufficient to perform all the requested tests. Which of the following actions should be performed?

Cancel all the cultures requested
Call the clinician to establish the priorities for the culture (Correct answer)
Establish the priorities for culture based on patient diagnosis
Decrease the sample volume per culture plate to ensure the full culture request is fulfilled

Correct answer: Call the clinician to establish the priorities for the culture

Explanation: When faced with an insufficient sample volume for requested tests, it's prudent to communicate with the clinician to determine the most critical cultures based on the patient's clinical presentation and suspected diagnosis. This ensures that limited resources are directed toward the most relevant tests, optimizing patient care.

Question 24: An ABO discrepancy is observed in a 75-year-old patient. The forward grouping shows Anti-A: 4+, Anti-B: 0. The reverse grouping shows A1 cells: 0, B cells: 1+. An autocontrol is negative. What is the most probable cause of this discrepancy?

A subgroup of A
Rouleaux formation due to high protein levels
Presence of a cold autoantibody
Age-related decrease in anti-B antibody production (Correct answer)

Correct answer: Age-related decrease in anti-B antibody production

The forward type is clearly Group A. The reverse grouping confirms the absence of anti-A but shows a weak (1+) reaction with B cells. In elderly patients, it is common for isoagglutinin (antibody) titres, such as anti-B, to decrease, leading to weak or missing reactions in the reverse group. The negative autocontrol makes a cold autoantibody less likely.

Question 25: After automated tissue processing, a batch of cassettes feels soft and the tissue is greasy to the touch. During microtomy, the tissue crumbles and fails to form a ribbon. This is most likely due to incomplete action by which reagent?

Fixative (e.g., formalin)
Infiltrating paraffin
Clearing agent (e.g., xylene) (Correct answer)
Dehydrating alcohol

Correct answer: Clearing agent (e.g., xylene)

The clearing agent's purpose is to remove the dehydrating alcohol and make the tissue miscible with the molten paraffin wax. If the clearing step is incomplete, residual alcohol will prevent the paraffin from fully infiltrating the tissue. [28] This results in a soft, greasy block where the tissue is not properly supported, leading to crumbling upon sectioning. [19, 20, 23]

Question 26: The forward type of a patient is Group A, but the reverse type shows an unexpected reaction with A1 cells, suggesting Group O. The patient is a healthy 25-year-old blood donor. What is the most probable cause for this discrepancy?

The patient has an acquired B antigen.
There is rouleaux formation interfering with the test.
The patient has the Bombay phenotype (Oh).
The patient is an A2 subgroup with anti-A1. (Correct answer)

Correct answer: The patient is an A2 subgroup with anti-A1.

This discrepancy pattern is characteristic of an A2 individual who has produced an anti-A1 antibody. The patient's red cells are group A (specifically, A2 subgroup) and react with Anti-A. However, their plasma contains the expected anti-B and also an unexpected anti-A1, which reacts with the A1 cells used in the reverse grouping panel. This causes the reverse group to appear like that of a Group O individual. [2, 4, 11]

Question 27: What is the correct order for removing personal protective equipment (PPE) after working with potentially infectious specimens?

Eye protection, gloves, mask, gown
Gloves, gown, eye protection, mask (Correct answer)
Mask, eye protection, gown, gloves
Gown, mask, gloves, eye protection

Correct answer: Gloves, gown, eye protection, mask

Gloves are removed first because they are the most contaminated item. The gown follows, then eye protection and mask, minimizing the risk of self-contamination during removal.

Question 28: Which of the following enzymes is most specific for assessing acute pancreatitis?

Alanine aminotransferase (ALT)
Amylase (AMY)
Lipase (LPS) (Correct answer)
Creatine kinase (CK)

Correct answer: Lipase (LPS)

While both amylase and lipase levels rise in acute pancreatitis, lipase is considered more specific. Amylase can be elevated in other conditions (e.g., salivary gland disorders, renal failure). Lipase remains elevated for a longer period than amylase, making it more useful for diagnosis, especially if presentation is delayed.

Question 29: A Gram-positive coccus, growing in chains, is isolated from a throat swab. It is beta-hemolytic and catalase-negative. A rapid PYR test is performed and yields a bright cherry-red color. Which organism is most likely present?

Streptococcus pneumoniae
Streptococcus agalactiae
Streptococcus pyogenes (Correct answer)
Staphylococcus saprophyticus

Correct answer: Streptococcus pyogenes

*Streptococcus pyogenes* (Group A Streptococcus) is a primary cause of bacterial pharyngitis. It is beta-hemolytic, catalase-negative, and gives a positive result in the PYR (pyrrolidonyl arylamidase) test, which produces a red color. *Streptococcus agalactiae* is PYR-negative. *Streptococcus pneumoniae* is alpha-hemolytic and PYR-negative. *Staphylococcus saprophyticus* is catalase-positive.

Question 30: Which of the following factors is a possible cause for cocci in chains to appear pink on a gram stain?

The patient has a high WBC count
The slides were flooded with crystal violet for one minute
The slide was flooded with iodine for two minutes
The patient is on antibiotics (Correct answer)

Correct answer: The patient is on antibiotics

Explanation: Antibiotic use can affect the cell wall of bacteria, leading to altered staining characteristics. In the case of cocci in chains appearing pink on a Gram stain, it suggests that the bacteria may have lost their ability to retain the crystal violet dye due to antibiotic-induced changes in cell wall structure.

Question 31: What is the principle of the Jaffe reaction for measuring creatinine?

Creatinine is measured directly using an ion-selective electrode.
Urease converts urea to ammonia, and the resulting change in conductivity is measured.
An enzymatic reaction using creatininase produces a colored product measured spectrophotometrically.
Creatinine reacts with picric acid in an alkaline solution to form a red-orange complex. (Correct answer)

Correct answer: Creatinine reacts with picric acid in an alkaline solution to form a red-orange complex.

The Jaffe reaction, a long-standing method for creatinine measurement, is based on the principle that creatinine reacts with picrate ions in an alkaline medium to form a reddish-orange complex. The rate of color formation is proportional to the creatinine concentration.

Question 32: What reagent is applied prior to the counterstain in a gram stain procedure?

Decolourizer (Correct answer)
Safranin
Mordant
Saline

Correct answer: Decolourizer

Explanation: In a Gram stain procedure, the decolourizer is applied after the primary stain (crystal violet) and prior to the counterstain (safranin). Its purpose is to remove the primary stain from gram-negative bacteria while allowing the retention of the stain by gram-positive bacteria.

Question 33: An isolate from a wound infection shows Gram-positive cocci in pairs and chains. The organism is catalase-negative and grows on bile esculin agar, turning the slant black. It also demonstrates growth in 6.5% NaCl broth. What is the most probable identification?

Streptococcus bovis group
Streptococcus agalactiae
Streptococcus pyogenes
Enterococcus faecalis (Correct answer)

Correct answer: Enterococcus faecalis

The ability to hydrolyze esculin in the presence of bile (turning the agar black) and to tolerate a high salt concentration (growth in 6.5% NaCl) are hallmark characteristics of the genus *Enterococcus*. While some Group D streptococci (like the *Streptococcus bovis* group) are bile esculin positive, they do not grow in 6.5% NaCl. *S. pyogenes* and *S. agalactiae* are negative for both tests.

Question 34: Normal CSF total protein is approximately:

0.15–0.45 g/L (Correct answer)
1.5–4.5 g/L
Less than 0.05 g/L
5–10 g/L

Correct answer: 0.15–0.45 g/L

Normal CSF total protein ranges from 0.15 to 0.45 g/L, which is much lower than plasma protein levels due to the blood-brain barrier.

Question 35: Which of the following is an important pre-analytical consideration when interpreting thyroid function tests during pregnancy?

Thyroid peroxidase antibodies are always negative in a normal pregnancy.
TSH levels are expected to be higher throughout pregnancy.
Trimester-specific reference intervals should be used for TSH and free T4. (Correct answer)
Only total T4 should be used as free T4 is unreliable.

Correct answer: Trimester-specific reference intervals should be used for TSH and free T4.

During pregnancy, physiological changes significantly alter thyroid hormone levels. For example, hCG can weakly stimulate the TSH receptor, leading to lower TSH levels, particularly in the first trimester. Additionally, estrogen increases thyroxine-binding globulin, affecting total hormone levels. Therefore, it is crucial to interpret TSH and free T4 results using trimester-specific reference intervals to accurately assess thyroid status.

Question 36: A clinical microbiology laboratory adopts MALDI-TOF MS for routine bacterial identification. What is the underlying principle of this technology?

Determination of fatty acid methyl esters (FAME) by gas chromatography
Measurement of enzymatic activity through colorimetric substrate changes
Analysis of ribosomal protein profiles by mass spectrometry (Correct answer)
Detection of specific nucleic acid sequences using fluorescent probes

Correct answer: Analysis of ribosomal protein profiles by mass spectrometry

Matrix-Assisted Laser Desorption/Ionization Time-of-Flight Mass Spectrometry (MALDI-TOF MS) identifies microorganisms by analyzing the mass of their proteins. A laser strikes a mixture of the organism and a matrix, causing the proteins (primarily ribosomal proteins) to ionize and travel through a vacuum tube. The time it takes for these ions to reach the detector is measured, which corresponds to their mass-to-charge ratio. This creates a unique proteomic fingerprint that is compared to a database for identification.

Question 37: Which of the following is the most appropriate method for sterilizing a heat-sensitive solution containing antibiotics for use in culture media?

Autoclaving at 121°C for 15 minutes
Exposure to ultraviolet (UV) radiation for 30 minutes
Filtration through a 0.22 µm pore size membrane (Correct answer)
Boiling at 100°C for 10 minutes

Correct answer: Filtration through a 0.22 µm pore size membrane

Heat-sensitive solutions, such as those containing antibiotics, vitamins, or certain sugars, will be degraded by the high temperatures of an autoclave. The most appropriate method for sterilizing these liquids is filtration. Using a membrane filter with a pore size of 0.22 micrometers will effectively remove bacteria and fungal spores without altering the chemical composition of the solution. The other methods involve heat or radiation which would destroy the heat-labile components.

Question 38: Which of the following scenarios would most likely result in a mixed-field reaction in the forward ABO grouping?

A Group B patient recently transfused with Group O red blood cells. (Correct answer)
A Group O patient with a strong cold autoantibody.
A Group AB patient with multiple myeloma.
A Group A patient with hypogammaglobulinemia.

Correct answer: A Group B patient recently transfused with Group O red blood cells.

A mixed-field reaction shows two distinct cell populations: one agglutinated and one unagglutinated. This is a hallmark of a recent transfusion with a different, compatible ABO group. A Group B patient receiving Group O red cells will have both their own B-antigen-positive cells (which will agglutinate with Anti-B) and the transfused O cells (which will not), creating a mixed-field appearance. [3, 4, 11]

Question 39: A titer of 1:320 compared to 1:40 for the same patient indicates:

No significant change
Lower antibody concentration in the 1:320 sample
A false-positive result
Higher antibody concentration in the 1:320 sample (Correct answer)

Correct answer: Higher antibody concentration in the 1:320 sample

A titer of 1:320 reflects a higher dilution needed to reduce reactivity, indicating a greater concentration of antibody than a titer of 1:40.

Question 40: Which electrophoresis technique is best suited for separating very large DNA fragments greater than 50 kilobases?

Capillary electrophoresis
Pulsed-field gel electrophoresis (PFGE) (Correct answer)
Polyacrylamide gel electrophoresis
Agarose gel electrophoresis

Correct answer: Pulsed-field gel electrophoresis (PFGE)

PFGE uses alternating electrical fields that cause large DNA molecules to reorient and migrate differently, enabling resolution of fragments up to several megabases that co-migrate in standard agarose electrophoresis.

Question 41: High-resolution melt (HRM) analysis detects sequence variants by monitoring:

Differences in fragment size after restriction digestion
Fluorescence emitted by a sequence-specific TaqMan probe
Changes in the melting profile of PCR products as they are heated (Correct answer)
Hybridization intensity of labeled probes on a microarray

Correct answer: Changes in the melting profile of PCR products as they are heated

HRM monitors the decrease in fluorescence as double-stranded PCR product is denatured by increasing temperature; mutations alter base pairing and change the shape or temperature of the melt curve compared to wild-type.

Question 42: The lecithin-to-sphingomyelin (L/S) ratio in amniotic fluid is used to assess:

Fetal kidney maturity
Fetal lung maturity (Correct answer)
Placental function
Risk of Down syndrome

Correct answer: Fetal lung maturity

An L/S ratio ≥2.0 indicates fetal lung maturity and a reduced risk of neonatal respiratory distress syndrome.

Question 43: The negative predictive value (NPV) of a molecular diagnostic test describes:

The proportion of diseased patients who test positive
The probability that a positive result is a true positive
The proportion of all tested patients who are truly negative
The probability that a negative result correctly means the patient is disease-free (Correct answer)

Correct answer: The probability that a negative result correctly means the patient is disease-free

NPV is the probability that a patient with a negative test result truly does not have the condition; it is influenced by both the specificity of the test and the prevalence of the disease in the tested population.

Question 44: Rheumatoid factor (RF) is an autoantibody directed against:

Platelet glycoproteins
Nuclear antigens
Double-stranded DNA
The Fc portion of IgG (Correct answer)

Correct answer: The Fc portion of IgG

Rheumatoid factor is an autoantibody, typically IgM, that targets the Fc region of IgG immunoglobulins.

Question 45: What is the purpose of running quality control (QC) samples in a medical laboratory?

To reduce the cost of reagent consumption
To train new laboratory technologists on procedures
To test new equipment before purchase
To verify that analytical instruments and reagents are producing accurate and reliable results (Correct answer)

Correct answer: To verify that analytical instruments and reagents are producing accurate and reliable results

Quality control samples with known values are analyzed alongside patient specimens to detect errors in the analytical process, ensuring that patient results are accurate and clinically reliable.

Question 46: A laboratory is implementing a new automated immunoassay analyzer. To verify the new method's performance, the lab sends 50 patient samples to a reference laboratory that uses the established 'gold standard' method. The results from both analyzers are then compared. This process is primarily assessing which of the following performance characteristics?

Sensitivity
Linearity
Precision
Accuracy (Correct answer)

Correct answer: Accuracy

Accuracy, sometimes called trueness, is the measure of how closely a test result agrees with an accepted reference value or a 'gold standard' method. [23, 24] By comparing the new analyzer's results to those from the reference method, the laboratory is evaluating the accuracy of the new system. Precision refers to the reproducibility of results when the same sample is tested multiple times. [15, 22]

Question 47: Which of the following actions minimizes injury due to excessive pipetting?

Rotating pipetting task with other duties (Correct answer)
Using a positive displacement technique
Keeping all the samples at arm’s length reach
Adjusting the workstation so that arms are elevated

Correct answer: Rotating pipetting task with other duties

Explanation: Rotating pipetting tasks with other duties helps minimize injury due to excessive pipetting by reducing prolonged repetitive motions. Alternating between tasks allows for periods of rest and recovery for the hands and fingers, decreasing the risk of repetitive strain injuries.

Question 48: A laboratory in Alberta is following a common two-step algorithm for the diagnosis of Clostridioides difficile infection (CDI) from a stool sample. The first step is a screening test for Glutamate Dehydrogenase (GDH) antigen, which is positive. What is the most appropriate second step to confirm active, toxin-producing CDI?

Culture the organism on cycloserine-cefoxitin-fructose agar (CCFA)
Perform a cell culture cytotoxicity assay
Repeat the GDH antigen test on a new sample
Perform a nucleic acid amplification test (NAAT) for the toxin B gene (tcdB) (Correct answer)

Correct answer: Perform a nucleic acid amplification test (NAAT) for the toxin B gene (tcdB)

In Canadian laboratories, a common algorithm for C. difficile testing involves a sensitive screening test followed by a specific confirmatory test. A positive GDH antigen test indicates the presence of the C. difficile organism but does not confirm toxin production. Therefore, a positive screen must be followed by a test that specifically detects the toxin or the gene responsible for its production. A nucleic acid amplification test (NAAT), such as PCR for the tcdB gene, is the recommended and widely used confirmatory step to detect toxigenic C. difficile.

Question 49: In quantitative real-time PCR (qPCR), what does the Ct (cycle threshold) value represent?

The cycle at which fluorescence crosses the detection threshold (Correct answer)
The concentration of primers in the reaction
The melting temperature of the amplified product
The total number of PCR cycles programmed

Correct answer: The cycle at which fluorescence crosses the detection threshold

The Ct value is the PCR cycle number at which the fluorescence signal rises above background threshold; a lower Ct indicates a higher initial amount of target nucleic acid.

Question 50: Which of the following actions should be taken when tissue sections stained with hematoxylin and eosin show pale cytoplasmic staining?

Check the pH of the eosin and adjust the sodium hydroxide if necessary
Check the pH of eosin and adjust with acetic acid if necessary (Correct answer)
Return the slides to the bluing reagent
Use heat during the staining process

Correct answer: Check the pH of eosin and adjust with acetic acid if necessary

Explanation: Eosin is an acidic dye, and its pH affects the staining quality. If tissue sections show pale cytoplasmic staining, it indicates potential issues with eosin staining. Checking the pH of eosin and adjusting it with acetic acid if necessary can help restore optimal staining conditions, leading to improved cytoplasmic staining in histological specimens.

Question 51: An Oral Glucose Tolerance Test (OGTT) is performed on a non-pregnant adult. A fasting glucose of 6.8 mmol/L and a 2-hour post-load glucose of 11.5 mmol/L is obtained. According to Canadian Diabetes Association guidelines, this is indicative of:

Diabetes mellitus (Correct answer)
Impaired fasting glucose (IFG)
Impaired glucose tolerance (IGT)
Normal glucose tolerance

Correct answer: Diabetes mellitus

A 2-hour plasma glucose value of ≥ 11.1 mmol/L during an OGTT is diagnostic for diabetes mellitus. While the fasting glucose is in the impaired fasting glucose range (6.1-6.9 mmol/L), the 2-hour value meets the criteria for a diagnosis of diabetes.

Question 52: A cervical cytology report describes squamous cells with significant nuclear enlargement, perinuclear halos, and nuclear membrane irregularities (koilocytotic atypia). According to the Bethesda System, this finding is characteristic of which interpretation?

Negative for Intraepithelial Lesion or Malignancy (NILM)
High-grade Squamous Intraepithelial Lesion (HSIL)
Low-grade Squamous Intraepithelial Lesion (LSIL) (Correct answer)
Atypical Squamous Cells of Undetermined Significance (ASC-US)

Correct answer: Low-grade Squamous Intraepithelial Lesion (LSIL)

Koilocytes are the hallmark cellular changes associated with the cytopathic effects of Human Papillomavirus (HPV). [6, 34] The Bethesda System for Reporting Cervical Cytology classifies changes consistent with HPV infection, including koilocytotic atypia, as a Low-grade Squamous Intraepithelial Lesion (LSIL). [6, 21]

Question 53: Restriction fragment length polymorphism (RFLP) analysis detects genetic variation by:

Identifying sequence changes that create or abolish restriction enzyme recognition sites (Correct answer)
Measuring differences in gene expression between individuals
Quantifying copy number variants by real-time PCR
Detecting chromosomal translocations with fluorescent probes

Correct answer: Identifying sequence changes that create or abolish restriction enzyme recognition sites

RFLP detects sequence polymorphisms where a nucleotide change creates or destroys a restriction site, producing fragments of different sizes that are separated and visualized by electrophoresis.

Question 54: Which serological test is the gold standard for confirming HIV infection?

Immunofluorescence
ELISA
Western blot (Correct answer)
Latex agglutination

Correct answer: Western blot

Western blot is used as the confirmatory test for HIV infection because it detects antibodies to specific viral proteins.

Question 55: Proteinuria detected on a urine dipstick is most sensitive for:

Tamm-Horsfall protein
Bence Jones protein
Albumin (Correct answer)
Globulins

Correct answer: Albumin

The urine dipstick protein reaction uses a pH indicator dye that is most sensitive to albumin and may miss other protein types.

Question 56: SYBR Green dye in qPCR generates signal by:

Fluorescing when cleaved by the 5'-to-3' exonuclease activity of Taq
Hybridizing to a specific probe sequence on the amplicon
Intercalating into any double-stranded DNA formed during amplification (Correct answer)
Binding specifically to the primer-template junction

Correct answer: Intercalating into any double-stranded DNA formed during amplification

SYBR Green intercalates non-specifically into any double-stranded DNA, producing fluorescence proportional to the amount of double-stranded PCR product accumulated.

Question 57: Oval fat bodies seen in urine microscopy are associated with:

Pyelonephritis
Acute tubular necrosis
Urinary tract infection
Nephrotic syndrome (Correct answer)

Correct answer: Nephrotic syndrome

Oval fat bodies are renal tubular cells or macrophages containing absorbed lipids and are characteristic of nephrotic syndrome.

Question 58: What is the systematic approach to reviewing a task or job to identify hazards?

Internal audit
Hazard control
Risk assessment (Correct answer)
Administrative control

Correct answer: Risk assessment

Explanation: Risk assessment is the systematic approach to reviewing a task or job to identify hazards. It involves evaluating the likelihood and severity of potential hazards and implementing measures to mitigate risks. By conducting risk assessments, laboratories can proactively identify and address potential safety concerns, promoting a safe working environment for staff and patients.

Question 59: A lymph node biopsy is submitted for routine H&E staining and may also require future immunohistochemistry (IHC). Which of the following is the most appropriate and widely used fixative for this purpose?

Carnoy's fixative
Bouin's solution
10% Neutral Buffered Formalin (NBF) (Correct answer)
Zenker's fluid

Correct answer: 10% Neutral Buffered Formalin (NBF)

10% Neutral Buffered Formalin (NBF) is the gold standard for routine histology because it provides excellent preservation of tissue morphology and is compatible with the vast majority of immunohistochemical stains. [10, 24, 25] While other fixatives have specific uses, NBF offers the best balance of morphological detail and antigen preservation for both H&E and subsequent IHC studies. [25, 27]

Question 60: Pleural fluid with a protein concentration greater than 30 g/L is classified as:

Exudate (Correct answer)
Transudate
Hemothorax
Chylous effusion

Correct answer: Exudate

Exudates have protein greater than 30 g/L (or LDH-based Light's criteria), indicating inflammation, infection, or malignancy as the cause.

Question 61: What is the primary purpose of the denaturation step in PCR?

To separate double-stranded DNA into single strands (Correct answer)
To remove RNA contamination from the sample
To synthesize new DNA strands using polymerase
To allow primers to bind to the template

Correct answer: To separate double-stranded DNA into single strands

Denaturation at 94–96°C breaks the hydrogen bonds between complementary base pairs, separating the double-stranded DNA into single-stranded templates for subsequent primer annealing.

Question 62: Allele-specific PCR (AS-PCR) is designed primarily to:

Detect specific single nucleotide variants or point mutations (Correct answer)
Amplify the entire coding sequence of a gene
Compare expression levels between two tissue types
Identify gene fusions in hematological malignancies

Correct answer: Detect specific single nucleotide variants or point mutations

AS-PCR uses a primer whose 3' end matches only the target allele; amplification occurs exclusively when the primer perfectly hybridizes to that variant, enabling sensitive detection of specific SNPs or mutations.

Question 63: Which immunoglobulin class is the first to be produced during a primary immune response?

IgG
IgE
IgA
IgM (Correct answer)

Correct answer: IgM

IgM is the first antibody produced during a primary immune response due to its pentameric structure enabling early complement activation.

Question 64: A patient has a prolonged activated partial thromboplastin time (APTT). A 1:1 mixing study is performed. The immediate APTT on the mix corrects into the normal range, but after a 2-hour incubation at 37°C, the APTT of the mixture becomes prolonged again. This pattern is most characteristic of:

A time- and temperature-dependent inhibitor, such as anti-Factor VIII (Correct answer)
Heparin contamination
Lupus anticoagulant
Factor V deficiency

Correct answer: A time- and temperature-dependent inhibitor, such as anti-Factor VIII

The initial correction of the APTT upon mixing with normal plasma suggests a factor deficiency. However, the subsequent prolongation after incubation indicates the presence of an inhibitor that requires time and temperature to inactivate the corresponding factor in the normal plasma. This is the classic presentation of a specific factor inhibitor, most commonly against Factor VIII.

Question 65: A patient is diagnosed with Graves' disease. What is the characteristic pattern of thyroid function test results expected in this patient?

High TSH, Low Free T4
Low TSH, High Free T4 (Correct answer)
Low TSH, Low Free T4
High TSH, High Free T4

Correct answer: Low TSH, High Free T4

Graves' disease is an autoimmune disorder where thyroid-stimulating immunoglobulins (TSI) bind to and activate the TSH receptor, leading to excessive thyroid hormone production (hyperthyroidism). This results in high levels of Free T4 and T3. The high levels of thyroid hormones, in turn, suppress the pituitary's production of TSH through negative feedback, leading to a low or undetectable TSH level.

Question 66: In a latex agglutination test, the latex particles are coated with:

EDTA anticoagulant
Known antigen or antibody specific for the analyte being tested (Correct answer)
Patient serum
Saline only

Correct answer: Known antigen or antibody specific for the analyte being tested

Latex particles are coated with a known antigen or antibody so they agglutinate visibly when the complementary analyte is present in the patient sample.

Question 67: Which of the following Gram-positive cocci is a key pathogen known for being catalase-positive, coagulase-positive, and often beta-hemolytic on blood agar?

Streptococcus pyogenes
Staphylococcus aureus (Correct answer)
Staphylococcus epidermidis
Enterococcus faecium

Correct answer: Staphylococcus aureus

*Staphylococcus aureus* is distinguished from other staphylococci by its production of coagulase, an enzyme that clots plasma. It is also catalase-positive, which differentiates it from streptococci and enterococci. Many strains of *S. aureus* produce hemolysins that cause beta-hemolysis on blood agar.

Question 68: A medical laboratory technologist is analyzing a culture from a urine sample of a 22-year-old female patient with symptoms of a urinary tract infection. The Gram stain reveals Gram-positive cocci in clusters. The organism is catalase-positive and coagulase-negative. Which of the following tests is most crucial for the presumptive identification of Staphylococcus saprophyticus?

Bile esculin hydrolysis
Novobiocin susceptibility (Correct answer)
Bacitracin susceptibility
PYR (pyrrolidonyl arylamidase) test

Correct answer: Novobiocin susceptibility

*Staphylococcus saprophyticus* is a common cause of urinary tract infections in young, sexually active females. A key characteristic that differentiates it from other coagulase-negative staphylococci, such as *Staphylococcus epidermidis*, is its resistance to the antibiotic novobiocin. Bacitracin is used for streptococci, bile esculin for enterococci and Group D streptococci, and PYR is primarily for *Enterococcus* and *Streptococcus pyogenes*.

Question 69: Which antinuclear antibody (ANA) pattern is most associated with systemic lupus erythematosus (SLE)?

Homogeneous (diffuse) (Correct answer)
Speckled
Nucleolar
Centromere

Correct answer: Homogeneous (diffuse)

The homogeneous (diffuse) ANA pattern is most commonly associated with SLE and correlates with anti-dsDNA and anti-histone antibodies.

Question 70: An RhD-negative mother has just delivered an RhD-positive infant. The mother's antibody screen is negative. According to Canadian guidelines, what is the primary purpose of administering Rh Immune Globulin (RhIG) to the mother within 72 hours?

To treat any potential hemolytic disease in the current newborn
To prevent the mother from forming anti-D that could affect future RhD-positive pregnancies (Correct answer)
To suppress the mother's existing anti-D antibodies
To clear passive anti-D from a previous antenatal injection

Correct answer: To prevent the mother from forming anti-D that could affect future RhD-positive pregnancies

Postpartum RhIG provides passive anti-D to the mother. This passive antibody binds to and clears any RhD-positive fetal red cells that may have entered her circulation during delivery, preventing her immune system from recognizing the D antigen and becoming actively immunized. This protects future RhD-positive fetuses from Hemolytic Disease of the Fetus and Newborn.

Question 71: In Southern blotting, why is the gel treated with alkali after electrophoresis?

To neutralize the gel before probe hybridization
To digest non-target DNA before transfer to the membrane
To denature double-stranded DNA into single strands before transfer (Correct answer)
To stain DNA bands for direct visualization

Correct answer: To denature double-stranded DNA into single strands before transfer

Alkali denaturation converts the double-stranded DNA in the gel into single strands; single-stranded DNA is then transferred to a membrane where it can hybridize with a complementary labeled probe.

Question 72: The complement pathway initiated by antigen-antibody complexes is the:

Propyl pathway
Classical pathway (Correct answer)
Lectin pathway
Alternative pathway

Correct answer: Classical pathway

The classical complement pathway is activated by antigen-antibody (immune) complexes binding to C1q.

Question 73: A Levey-Jennings chart for a daily glucose control shows that the last seven consecutive data points are all above the mean, but still within the ±2 SD limits. According to Westgard multirule procedures, what does this pattern indicate?

A random error
An acceptable run as no points are outside ±2 SD
A 2_2s rule violation
A systematic error, specifically a trend (Correct answer)

Correct answer: A systematic error, specifically a trend

This pattern describes a trend, which is a type of systematic error where results consistently move in one direction over a period of time. [6] A common Westgard rule (e.g., 7_T) identifies this pattern. It signals a gradual change in the testing system, such as reagent degradation or instrument calibration drift. A 2_2s rule is when two consecutive points exceed the same +2SD or -2SD limit. Random error would show no discernible pattern. Because a specific rule is violated, the run is not automatically acceptable and requires investigation. [8, 18]

Question 74: Which of the following specimen orders prioritizes the processing of microbiology specimens correctly?

Blood culture, CSF, unpreserved stool, stool in transport media
CSF, swab in transport media, surgical specimens, unpreserved stool
CSF, blood culture, urine, swab in transport media (Correct answer)
Rapid antigen testing, CSF, urine, stool in transport media

Correct answer: CSF, blood culture, urine, swab in transport media

Explanation: When prioritizing the processing of microbiology specimens, it is essential to consider factors such as urgency and specimen stability. CSF and blood cultures are typically considered urgent specimens due to their clinical significance, followed by urine and swabs in transport media. This order ensures the timely processing of critical specimens while maintaining the integrity of the samples.

Question 75: A patient presents with hypertension, headaches, and palpitations. The physician suspects a pheochromocytoma. Which of the following laboratory tests is considered the most sensitive for confirming this diagnosis?

Total urinary catecholamines
Urinary vanillylmandelic acid (VMA)
Plasma catecholamines
Plasma free metanephrines (Correct answer)

Correct answer: Plasma free metanephrines

Plasma free metanephrines are metabolites of catecholamines (epinephrine and norepinephrine) and are produced continuously within a pheochromocytoma. Their measurement has the highest sensitivity for detecting these tumors, often considered the test of first choice. While other tests like urinary VMA and catecholamines are used, they have lower sensitivity compared to plasma free metanephrines.

Question 76: A patient's forward grouping shows agglutination with Anti-A and weak (1+) agglutination with Anti-B. The reverse grouping shows agglutination with B cells only. The patient's diagnosis is a severe gastrointestinal infection caused by a gram-negative bacteria. What is the MOST likely cause of this ABO discrepancy?

Cold autoantibody interference
Acquired B antigen (Correct answer)
A subgroup with anti-B alloantibody
Recent transfusion of group B red cells

Correct answer: Acquired B antigen

The 'Acquired B' phenomenon occurs in group A individuals, often with gastrointestinal diseases or gram-negative septicemia. Bacterial enzymes modify the A antigen (N-acetyl-D-galactosamine) to a structure that resembles the B antigen (D-galactose), causing a weak reaction with some anti-B reagents. [2, 6, 8] The patient's own anti-B does not react with this 'B-like' antigen, so the reverse group is consistent with a group A individual. [6, 8]

Question 77: A prozone phenomenon in agglutination testing occurs when:

Temperature is too high
Antibody is in excess causing false-negative results (Correct answer)
Antigen is in excess causing false-negative results
pH is too acidic

Correct answer: Antibody is in excess causing false-negative results

The prozone effect occurs when antibody excess prevents lattice formation, resulting in a false-negative agglutination reaction.

Question 78: Which of the following actions should be taken when the hematoxylin and eosin stain lacks three distinct shades of pink?

Increase time in water
Check the pH of fixative
Check the pH of eosin (Correct answer)
Replace hematoxylin

Correct answer: Check the pH of eosin

Explanation: In histotechnology, the quality of staining is crucial for accurate tissue examination. Checking the pH of eosin is important because an incorrect pH level can affect the staining process and result in inadequate differentiation of tissue components, such as lacking distinct shades of pink in the eosin stain. Adjusting the pH can help ensure proper staining and interpretation of tissue samples.

Question 79: A gynecological smear is stained using the Papanicolaou method. Which cellular component is specifically highlighted by the Orange G (OG-6) solution?

Cytoplasm of mature, keratinized squamous cells. (Correct answer)
Cilia and red blood cells.
Nuclei of immature parabasal cells.
Cytoplasm of metabolically active cells like intermediate cells.

Correct answer: Cytoplasm of mature, keratinized squamous cells.

In the Papanicolaou stain, Orange G (OG-6) is an acidic counterstain that has a high affinity for keratin. It specifically stains the cytoplasm of mature, superficial squamous cells, which are often keratinized, a distinct orange-yellow color. [9, 13] Hematoxylin stains the nuclei, while the Eosin Azure (EA) component provides differential staining for the cytoplasm of less mature cells. [13]

Question 80: Synovial fluid from a patient with gout would typically show:

No crystals
Only white blood cells
Negatively birefringent needle-shaped crystals under polarized light (Correct answer)
Positively birefringent rhomboid crystals

Correct answer: Negatively birefringent needle-shaped crystals under polarized light

Gout is characterized by negatively birefringent, needle-shaped monosodium urate crystals identified under compensated polarized light microscopy.

Question 81: Which of the following actions should be completed when blood culture specimens are being improperly collected?

Evaluate collection method (Correct answer)
Implement a solution
Reprimand employees
Perform employee evaluations

Correct answer: Evaluate collection method

Explanation: When blood culture specimens are improperly collected, the first step is to evaluate the collection method to identify the specific issues causing the problem. This may involve assessing training protocols, specimen collection techniques, or compliance with established procedures. Once the root cause is identified, appropriate solutions can be implemented to improve specimen collection practices and ensure accurate results.

Question 82: In a direct Coombs (DAT) test, a positive result indicates:

Antibodies or complement bound to red blood cells in vivo (Correct answer)
Free antibodies in serum
ABO incompatibility in vitro
Platelet antibodies present

Correct answer: Antibodies or complement bound to red blood cells in vivo

A positive direct antiglobulin test (DAT) indicates that antibodies or complement proteins are already coating the patient's red blood cells in vivo.

Question 83: What is the purpose of an internal control in a molecular diagnostic assay?

To detect PCR inhibition and confirm successful nucleic acid extraction (Correct answer)
To calculate the exact copy number of the pathogen
To identify any contaminating organisms in the sample
To set the fluorescence threshold for Ct determination

Correct answer: To detect PCR inhibition and confirm successful nucleic acid extraction

An internal control is co-extracted and co-amplified with the clinical sample; if it fails to amplify, this indicates either extraction failure or PCR inhibition, preventing false-negative reporting.

Question 84: In peritoneal (ascitic) fluid analysis, a serum-ascites albumin gradient (SAAG) ≥11 g/L indicates:

Portal hypertension (Correct answer)
Nephrotic syndrome
Bacterial peritonitis
Malignancy

Correct answer: Portal hypertension

A SAAG ≥11 g/L indicates portal hypertension (e.g., cirrhosis), reflecting increased hydrostatic pressure as the cause of ascites.

Question 85: HLA typing in transplantation medicine is performed to:

Match donor and recipient tissue antigens to reduce rejection (Correct answer)
Identify ABO incompatibility
Screen for autoimmune disease
Detect blood group antigens

Correct answer: Match donor and recipient tissue antigens to reduce rejection

HLA (human leukocyte antigen) typing matches major histocompatibility complex antigens between donor and recipient to minimize transplant rejection.

Question 86: A tech runs a quality control for creatinine and the result is 2 standard deviations above the mean. According to Westgard rules, what is the most appropriate first step?

Repeat the control on the same vial. (Correct answer)
Open a new vial of control and repeat the measurement.
Recalibrate the instrument immediately.
Report patient results and document the QC deviation.

Correct answer: Repeat the control on the same vial.

A single control value exceeding 2 standard deviations (a 1-2s rule violation) serves as a warning. The most common cause is random error. The initial step is to repeat the measurement using the same vial of control material to see if the error was random and self-corrects. If it remains out, further investigation is needed.

Question 87: Fifteen minutes into a red blood cell transfusion, a patient develops fever, chills, hypotension, and reports red-coloured urine. The post-transfusion direct antiglobulin test (DAT) is positive. What is the most likely type of transfusion reaction?

Bacterial Contamination
Acute Hemolytic Transfusion Reaction (AHTR) (Correct answer)
Febrile Non-Hemolytic Reaction
Anaphylactic Reaction

Correct answer: Acute Hemolytic Transfusion Reaction (AHTR)

The combination of fever, chills, hypotension, hemoglobinuria (red urine), and a positive DAT strongly indicates an Acute Hemolytic Transfusion Reaction. This is a medical emergency caused by the rapid destruction of donor red blood cells by recipient antibodies, most often due to ABO incompatibility.

Question 88: Cross-reactivity in serological testing occurs when:

Complement is inactivated
Two identical antigens react with the same antibody
An antibody reacts with a different but structurally similar antigen (Correct answer)
The test temperature is incorrect

Correct answer: An antibody reacts with a different but structurally similar antigen

Cross-reactivity occurs when an antibody raised against one antigen also binds to a structurally similar but different antigen, potentially causing false positives.

Question 89: A dark brown pigment is noted on formalin-fixed, hematoxylin, and eosin-stained sections. What action can prevent this from occurring?

“Bread loaf" large sections
Increase fixation time
Treat sections with alcoholic picric acid
Maintain formalin at a neutral pH (Correct answer)

Correct answer: Maintain formalin at a neutral pH

Explanation: Maintaining formalin at a neutral pH helps prevent the formation of dark brown pigment on tissue sections during fixation. Acidic formalin can lead to excessive pigment formation, affecting the quality of staining and tissue interpretation. Therefore, ensuring the formalin solution remains at a neutral pH is essential for optimal tissue preservation and staining in histotechnology.

Question 90: A technologist performs ABO grouping on a 92-year-old patient. The results are: Anti-A: 0, Anti-B: 4+, A1 Cells: 0, B Cells: 1+. Which of the following is the most appropriate first step to resolve this discrepancy?

Use Dolichos biflorus lectin to test for A1 subgroup.
Perform an antibody screen to identify the unexpected antibody.
Wash the patient's red cells with warm saline and repeat the forward grouping.
Incubate the patient's plasma with reagent cells at room temperature or 4°C. (Correct answer)

Correct answer: Incubate the patient's plasma with reagent cells at room temperature or 4°C.

This is a Group 1 discrepancy, characterized by weak or missing antibodies in the reverse grouping. [4] This is common in elderly patients due to decreased antibody production. [4] To enhance the weak reaction, incubating the patient's plasma with the reagent A1 and B cells at lower temperatures (room temperature or 4°C) can help facilitate antibody binding and resolve the discrepancy. [2, 4]

Question 91: A technologist receives a cerebrospinal fluid (CSF) specimen in the microbiology lab from a suspected case of bacterial meningitis. The specimen is received at 3:00 PM and the Gram stain is performed immediately. The day shift ends at 4:00 PM. Which of the following actions is most critical regarding the culture of this specimen?

Immediately inoculate the specimen onto appropriate media, such as Chocolate and Blood agar, and place in a CO2 incubator. (Correct answer)
Refrigerate the specimen at 4°C until the next morning to ensure a fresh subculture.
Inoculate the culture plates and leave them at room temperature for the evening shift to incubate.
Perform an antigen detection test and wait for the results before setting up the culture.

Correct answer: Immediately inoculate the specimen onto appropriate media, such as Chocolate and Blood agar, and place in a CO2 incubator.

CSF is considered a critical, irreplaceable specimen. Potential pathogens that cause meningitis, such as Neisseria meningitidis and Streptococcus pneumoniae, are fastidious and sensitive to temperature changes. The specimen must be processed immediately upon receipt. Delay or improper storage (like refrigeration, which can kill N. meningitidis) can lead to false-negative culture results. Immediate inoculation onto appropriate enriched media (like Chocolate agar) and incubation in a CO2-enriched atmosphere is crucial for the recovery of these delicate organisms.

Question 92: A patient has a history of a clinically significant antibody, anti-K, but their current antibody screen is negative. Which of the following is the most appropriate crossmatch procedure to ensure safety?

No crossmatch is needed if O Negative units are provided.
A full antiglobulin (IAT) crossmatch using K-antigen negative donor units. (Correct answer)
Electronic crossmatch is acceptable because the current antibody screen is negative.
An immediate spin crossmatch to confirm ABO compatibility is sufficient.

Correct answer: A full antiglobulin (IAT) crossmatch using K-antigen negative donor units.

A history of a clinically significant antibody is critical information. Even if the antibody is currently undetectable, the patient could have an anamnestic response upon re-exposure. Therefore, antigen-negative units must be selected, and a full antiglobulin (IAT) crossmatch must be performed to ensure serological compatibility and detect any low-titer antibodies.

Question 93: According to Canadian Workplace Hazardous Materials Information System (WHMIS) 2015 guidelines, which hazard is represented by the pictogram showing an exclamation mark?

Corrosive damage to metals, skin, and eyes
May cause less serious health effects, such as skin/eye irritation or act as a skin sensitizer (Correct answer)
May cause or is suspected of causing serious long-term health effects (e.g., carcinogen)
Oxidizing hazard

Correct answer: May cause less serious health effects, such as skin/eye irritation or act as a skin sensitizer

The exclamation mark pictogram under WHMIS/GHS is used for hazards that are less severe than those indicated by the skull and crossbones or health hazard pictograms. It signifies hazards such as being an irritant (skin and eye), a skin sensitizer, causing acute toxicity (harmful), or having narcotic effects. [5, 17] The corrosion pictogram shows damage to materials and skin, the health hazard (exploding person) pictogram indicates serious long-term effects like carcinogenicity, and the flame over circle represents oxidizing hazards. [1]

Question 94: A physician is evaluating a patient with a low pre-test probability for venous thromboembolism (VTE). Which of the following laboratory tests is most useful for ruling out this condition?

Platelet Count
D-dimer (Correct answer)
Prothrombin Time (PT)
Fibrinogen Level

Correct answer: D-dimer

The D-dimer test measures a specific degradation product of a cross-linked fibrin clot. It has a high negative predictive value, meaning a normal or negative result in a patient with low clinical suspicion makes the presence of a recent major clot (like DVT or PE) highly unlikely. Its high sensitivity and low specificity make it an excellent test for exclusion, but not for confirmation, of VTE.

Question 95: What is the normal specific gravity range of urine in a healthy adult?

1.000–1.005
1.001–1.035 (Correct answer)
0.990–1.000
1.040–1.060

Correct answer: 1.001–1.035

Normal urine specific gravity ranges from 1.001 to 1.035, reflecting the kidney's ability to concentrate or dilute urine.

Question 96: What is the most important step in preventing infection?

Disinfecting surfaces
Hand washing (Correct answer)
Wearing gloves
Wearing N95 mask

Correct answer: Hand washing

Explanation: Hand washing is the most important step in preventing infection transmission in healthcare settings. Proper hand hygiene reduces the spread of pathogens from surfaces to patients or healthcare workers, significantly decreasing the risk of infections.

Question 97: What is the function of restriction endonucleases in molecular biology?

To remove RNA primers from newly synthesized DNA
To amplify specific DNA sequences using thermal cycling
To cleave double-stranded DNA at specific palindromic recognition sequences (Correct answer)
To join DNA fragments with complementary ends

Correct answer: To cleave double-stranded DNA at specific palindromic recognition sequences

Restriction endonucleases recognize short specific palindromic sequences and cut both DNA strands at or near those sites, producing defined fragments used in cloning, RFLP analysis, and restriction mapping.

Question 98: Loop-mediated isothermal amplification (LAMP) is advantageous over PCR in resource-limited settings because:

It provides higher sensitivity than real-time PCR
It amplifies target DNA at a constant temperature without thermal cycling equipment (Correct answer)
It requires no primers and works on any nucleic acid
It can sequence amplicons directly without electrophoresis

Correct answer: It amplifies target DNA at a constant temperature without thermal cycling equipment

LAMP amplifies target DNA at a constant 60–65°C using 4–6 primers recognizing 6–8 target regions, eliminating the need for a thermocycler and making it suitable for point-of-care or field testing.

Question 99: According to Clinical and Laboratory Standards Institute (CLSI) guidelines, which are broadly followed in Canada for antimicrobial susceptibility testing (AST), what is the primary purpose of performing quality control using ATCC reference strains?

To ensure the antimicrobial agents have not expired
To monitor the precision and accuracy of the test procedure (Correct answer)
To verify that patient isolates are correctly identified before testing
To determine the minimum inhibitory concentration (MIC) for new antibiotics

Correct answer: To monitor the precision and accuracy of the test procedure

Quality control in antimicrobial susceptibility testing, using well-characterized reference strains from the American Type Culture Collection (ATCC), is essential for monitoring the entire test system. This includes the performance of the media, the antimicrobial disks or solutions, incubation conditions, and the technologist's technique. By testing these stable strains with known susceptibility profiles, the laboratory can ensure the precision and accuracy of the results obtained for patient isolates. This is a core principle of quality management outlined by standards bodies like CLSI.

Question 100: Immunofluorescence microscopy uses antibodies conjugated to:

Radioactive isotopes
Fluorescent dyes (Correct answer)
Enzymes like HRP
Gold particles

Correct answer: Fluorescent dyes

Immunofluorescence uses antibodies labeled with fluorescent dyes (fluorochromes) that emit light when excited by specific wavelengths.

Question 101: What Westgard rule violation occurs when a single QC result falls outside 3 standard deviations from the mean?

1-3s rule violation (Correct answer)
2-2s rule violation
R-4s rule violation
4-1s rule violation

Correct answer: 1-3s rule violation

The 1-3s rule flags when one control observation exceeds ±3 standard deviations, indicating a random error. This is typically considered an immediate rejection criterion requiring investigation.

Question 102: A urine pH of 5.0 would be considered:

Acidic (Correct answer)
Neutral
Invalid
Alkaline

Correct answer: Acidic

A urine pH of 5.0 is acidic; normal urine pH ranges from 4.5 to 8.0, with values below 7.0 being acidic.

Question 103: Glucose in urine (glucosuria) typically appears when blood glucose exceeds the renal threshold of approximately:

10 mmol/L (Correct answer)
5.5 mmol/L
3.0 mmol/L
15 mmol/L

Correct answer: 10 mmol/L

Glucosuria occurs when blood glucose exceeds approximately 10 mmol/L (180 mg/dL), saturating the tubular reabsorption capacity.

Question 104: A medical laboratory technologist performs a Modified Hodge Test (MHT) to screen for carbapenemase production in a Klebsiella pneumoniae isolate. A distinct 'cloverleaf-like' pattern of indented growth of the indicator organism (E. coli ATCC 25922) is observed around the test streak. How should this result be interpreted?

The isolate possesses an AmpC beta-lactamase but not a carbapenemase
The isolate is positive for carbapenemase production (Correct answer)
The test is invalid due to over-inoculation of the indicator strain
The isolate is negative for carbapenemase production

Correct answer: The isolate is positive for carbapenemase production

The Modified Hodge Test (MHT) is a phenotypic method used to detect carbapenemase production. The principle is that if the test organism produces carbapenemase, it will hydrolyze the carbapenem antibiotic diffusing from the disk. This allows the carbapenem-susceptible indicator strain (E. coli ATCC 25922) to grow towards the disk in the area where the antibiotic has been inactivated. This enhanced growth creates a characteristic cloverleaf-shaped indentation, which indicates a positive result for carbapenemase production.

Question 105: The Periodic acid-Schiff (PAS) stain is fundamentally based on the oxidation of which chemical group to form aldehydes, which then react with the Schiff reagent?

Amino groups
Sulfhydryl groups
1,2-Glycols (Correct answer)
Phosphate groups

Correct answer: 1,2-Glycols

The principle of the PAS stain involves the use of periodic acid to selectively oxidize 1,2-glycol groups (vicinal diols) present in carbohydrates. [5] This oxidation breaks the carbon-carbon bond and creates two aldehyde groups. These aldehydes then react with the colorless Schiff reagent to produce a distinctive magenta color, highlighting structures rich in glycogen, mucins, and basement membranes. [4, 5, 11]

Question 106: A four-fold rise in antibody titer between acute and convalescent serum samples is considered diagnostic of:

Active or recent infection with the tested pathogen (Correct answer)
A non-specific immune response
Immunodeficiency
Passive immunity from transfusion

Correct answer: Active or recent infection with the tested pathogen

A four-fold or greater rise in antibody titer between acute and convalescent samples indicates active infection and seroconversion.

Question 107: 16S rRNA gene sequencing is considered the gold standard for bacterial species identification because:

It detects antibiotic resistance genes directly
The gene contains conserved primer-binding regions flanking variable species-identifying regions (Correct answer)
It can identify bacteria without prior culture
It amplifies only pathogenic bacteria

Correct answer: The gene contains conserved primer-binding regions flanking variable species-identifying regions

The 16S rRNA gene has conserved regions that allow universal primers to bind across all bacteria, flanking variable regions whose sequences differ enough between species to provide definitive identification.

Question 108: A batch of used, non-sharp, blood collection tubes containing clotted human blood must be discarded. According to Canadian Standards Association (CSA) guidelines and general biosafety principles, what is the correct disposal method?

In a designated, leak-proof biohazard bag/container for autoclaving or incineration. (Correct answer)
Pouring the contents down the sink and discarding tubes in the regular garbage.
In a yellow, puncture-resistant biohazard sharps container.
In a regular office garbage bin.

Correct answer: In a designated, leak-proof biohazard bag/container for autoclaving or incineration.

Human blood and body fluids are considered biohazardous waste. Non-sharp items contaminated with this waste, such as blood tubes, must be placed in designated, labeled, and leak-proof biohazard bags or containers for subsequent decontamination, typically by autoclaving or incineration. [28, 29] Regular garbage is incorrect due to the infectious risk. Sharps containers are specifically for items that can puncture skin, like needles. Disposing of blood down a sink is generally not permitted and is an unsafe practice.

Question 109: Which of the following quality system essentials includes processes for selecting and installing laboratory instruments?

Equipment (Correct answer)
Assessments
Continual improvement
Process management

Correct answer: Equipment

Explanation: The quality system essential "equipment" involves processes for selecting, installing, and maintaining laboratory instruments to ensure their proper functioning and accuracy. This includes validation, calibration, and regular maintenance procedures to uphold quality standards in laboratory testing.

Question 110: Why is Taq polymerase used in PCR instead of a standard DNA polymerase?

It can amplify RNA directly without reverse transcription
It is thermostable and survives repeated heating to 94°C (Correct answer)
It requires no cofactors or dNTPs
It has higher fidelity and fewer errors

Correct answer: It is thermostable and survives repeated heating to 94°C

Taq polymerase, derived from Thermus aquaticus, is thermostable and retains activity through the repeated high-temperature denaturation cycles required in PCR.

Question 111: Fluorescence in situ hybridization (FISH) is primarily used in molecular diagnostics to:

Amplify specific gene sequences for sequencing
Detect specific DNA sequences or chromosomal rearrangements in intact cells (Correct answer)
Quantify mRNA expression levels in tissue samples
Determine antibiotic resistance profiles of bacteria

Correct answer: Detect specific DNA sequences or chromosomal rearrangements in intact cells

FISH uses fluorescently labeled DNA probes that hybridize to complementary chromosomal sequences, enabling visualization of gene deletions, amplifications, or translocations directly in cells or tissue sections.

Question 112: The VDRL and RPR tests are used to screen for:

Rubella
HIV
Syphilis (Correct answer)
Hepatitis B

Correct answer: Syphilis

The VDRL (Venereal Disease Research Laboratory) and RPR (Rapid Plasma Reagin) are non-treponemal screening tests for syphilis.

Question 113: Which urine crystal is associated with alkaptonuria and turns dark upon standing?

Homogentisic acid crystals (Correct answer)
Leucine crystals
Cystine crystals
Tyrosine crystals

Correct answer: Homogentisic acid crystals

Homogentisic acid accumulates in alkaptonuria and oxidizes to a dark brown pigment (alkapton) when urine is exposed to air.

Question 114: What class of biological safety cabinet (BSC) is most commonly used for routine work with Risk Group 2 organisms in Canadian laboratories?

Class I
Class III
Laminar flow hood
Class II Type A2 (Correct answer)

Correct answer: Class II Type A2

Class II Type A2 BSCs provide both personnel and product protection through HEPA-filtered vertical laminar airflow, making them suitable for routine work with moderate-risk biological agents in clinical laboratories.

Question 115: In an enzyme-linked immunosorbent assay (ELISA), the signal is generated by:

A complement protein
An enzyme conjugated to an antibody (Correct answer)
A fluorescent dye attached to antigen
A radioactive isotope

Correct answer: An enzyme conjugated to an antibody

In ELISA, an enzyme-conjugated antibody reacts with a substrate to produce a measurable colorimetric, fluorescent, or luminescent signal.

Question 116: The normal white blood cell count in cerebrospinal fluid is:

10–20 cells/µL
0–5 cells/µL (Correct answer)
50–100 cells/µL
0–50 cells/µL

Correct answer: 0–5 cells/µL

Normal CSF contains 0–5 white blood cells per µL (predominantly lymphocytes); higher counts indicate inflammation or infection.

Question 117: Which of the following reagents is used as the mordant and oxidant in the Weigert's hematoxylin?

Ferric chloride (Correct answer)
Ammonium potassium
Aluminum potassium sulfate
Iodine

Correct answer: Ferric chloride

Explanation: In the Weigert's hematoxylin staining method, ferric chloride serves as the mordant and oxidant. It helps intensify the staining of nuclei with hematoxylin and promotes the formation of a complex that binds to cellular structures.

Question 118: In clinical transplantation, high-resolution HLA typing is most accurately performed by:

Complement-dependent cytotoxicity (CDC) testing
ELISA for anti-HLA antibodies
Sequence-based typing (SBT) or PCR-SSO (Correct answer)
Flow cytometric crossmatch

Correct answer: Sequence-based typing (SBT) or PCR-SSO

Sequence-based typing (SBT) and PCR with sequence-specific oligonucleotide probes (PCR-SSO) provide allele-level resolution of HLA genes, enabling precise matching of donors and recipients in transplantation.

Question 119: A patient sample for electrolyte analysis is noted to be severely hemolyzed. Which analyte would be most significantly falsely elevated?

Chloride (Cl-)
Potassium (K+) (Correct answer)
Sodium (Na+)
Bicarbonate (HCO3-)

Correct answer: Potassium (K+)

Potassium is the major intracellular cation. Hemolysis, the rupture of red blood cells, releases large amounts of potassium into the serum or plasma, causing a falsely elevated result that does not reflect the patient's true physiological state.

Question 120: A satellite clinic sends a lithium heparin tube for potassium analysis to the central hospital lab. The sample is delayed in transit for 8 hours and is not refrigerated. The resulting potassium level is 6.8 mmol/L (critically high), but the patient is asymptomatic. What is the most likely cause of this result?

Contamination from a lavender (EDTA) top tube.
Pseudohyperkalemia due to delayed centrifugation. (Correct answer)
A true critical result requiring immediate physician notification.
Hemolysis from an excessively small gauge needle used for collection.

Correct answer: Pseudohyperkalemia due to delayed centrifugation.

When whole blood is stored for an extended period at room temperature without being centrifuged, potassium leaks from the red blood cells into the plasma. [3, 9] This process, known as pseudohyperkalemia, falsely elevates the measured potassium level. The lack of patient symptoms strongly suggests a pre-analytical error rather than true hyperkalemia. While EDTA contamination and hemolysis also cause high potassium, the key factor in this scenario is the significant delay in processing. [7, 11]

Question 121: Which of the following disinfectants must not be placed in an autoclave due to the generation of unsafe gases?

Sodium phosphate
70% alcohol
Sodium hypochlorite (Correct answer)
Hydrogen peroxide

Correct answer: Sodium hypochlorite

Explanation: Sodium hypochlorite, commonly known as bleach, should not be placed in an autoclave due to the potential generation of unsafe gases such as chlorine gas. Autoclaving sodium hypochlorite can result in hazardous chemical reactions and pose risks to laboratory staff and equipment. Therefore, it is essential to follow proper disinfection protocols and avoid autoclaving sodium hypochlorite.

Question 122: Which next-generation sequencing (NGS) platform uses fluorescently labeled reversible terminator nucleotides incorporated one base at a time?

Illumina sequencing by synthesis (Correct answer)
Oxford Nanopore sequencing
Ion Torrent semiconductor sequencing
Pacific Biosciences SMRT sequencing

Correct answer: Illumina sequencing by synthesis

Illumina's sequencing-by-synthesis uses fluorescently labeled, reversible terminator dNTPs; after each base is incorporated and imaged, the terminator is cleaved to allow incorporation of the next nucleotide.

Question 123: A patient's sample run on a hematology analyzer at room temperature (22°C) produces an MCHC of 390 g/L and a very low RBC count. A peripheral smear shows large, irregular clumps of red blood cells. What is the most appropriate next step to obtain accurate CBC results?

Report the results with a comment about RBC agglutination
Request a new sample drawn in a sodium citrate tube
Perform a saline replacement procedure to correct for lipemia
Warm the sample to 37°C for 15-30 minutes and rerun (Correct answer)

Correct answer: Warm the sample to 37°C for 15-30 minutes and rerun

The combination of a high MCHC, low RBC count, and visible RBC agglutination on the smear is characteristic of cold agglutinin disease. The IgM antibodies responsible for this cause RBCs to clump at temperatures below body temperature, leading to spurious results from automated analyzers. Warming the sample to 37°C will cause the agglutinins to dissociate from the RBCs, allowing for an accurate count.

Question 124: A bone marrow transplant recipient requires a red blood cell transfusion. To prevent Transfusion-Associated Graft-Versus-Host Disease (TA-GVHD), which of the following component modifications is most critical?

Irradiated (Correct answer)
CMV Seronegative
Leukoreduced
Washed

Correct answer: Irradiated

Irradiation is the only method that inactivates donor T-lymphocytes, which are responsible for causing TA-GVHD in severely immunocompromised recipients, such as bone marrow transplant patients. While leukoreduction removes most white cells and CMV-seronegative units prevent cytomegalovirus transmission, they do not reliably prevent TA-GVHD.

Question 125: A patient is admitted with severe hyponatremia, low serum osmolality, and inappropriately concentrated urine (high urine osmolality). The patient is euvolemic. These findings are most consistent with which of the following conditions?

Syndrome of Inappropriate Antidiuretic Hormone (SIADH) (Correct answer)
Adrenal Insufficiency
Diabetes Mellitus
Diabetes Insipidus (DI)

Correct answer: Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

SIADH is characterized by excessive release of ADH, which causes the kidneys to retain too much water. This leads to dilutional hyponatremia (low serum sodium), low serum osmolality, and the excretion of concentrated urine (high urine osmolality) because the body is not appropriately excreting free water. In contrast, Diabetes Insipidus involves a lack of ADH action, leading to hypernatremia and dilute urine.

Question 126: Which immunoglobulin class is the primary antibody in secretions such as saliva and breast milk?

IgG
IgM
IgA (Correct answer)
IgD

Correct answer: IgA

Secretory IgA is the predominant immunoglobulin in mucosal secretions such as saliva, tears, and breast milk, providing local immunity.

Question 127: Which of the following actions may be taken to gather evidence when a new polymerase chain reaction methodology is being investigated for clinical use?

Perform a literature review (Correct answer)
Incorporate into staff performance reviews
Rely on personal knowledge
Ask co-workers for their opinions

Correct answer: Perform a literature review

Explanation: When investigating a new polymerase chain reaction (PCR) methodology for clinical use, performing a literature review is essential. This involves gathering evidence from peer-reviewed scientific literature to assess the methodology's validity, reliability, and clinical utility. A literature review helps inform decision-making, ensuring that evidence-based practices are followed in the laboratory.

Question 128: A peripheral blood smear review is triggered by a 'Nucleated RBC' flag on an automated hematology analyzer. The technologist counts 8 NRBCs per 100 WBCs. The analyzer reported a total WBC count of 12.0 x 10^9/L. What is the corrected WBC count?

13.0 x 10^9/L
11.5 x 10^9/L
11.1 x 10^9/L (Correct answer)
12.0 x 10^9/L

Correct answer: 11.1 x 10^9/L

Automated hematology analyzers using certain technologies can misclassify nucleated red blood cells (NRBCs) as white blood cells (WBCs) because both have nuclei. This leads to a falsely elevated WBC count. A manual differential and NRBC count allows for a mathematical correction using the formula: Corrected WBC = (Uncorrected WBC x 100) / (100 + Number of NRBCs/100 WBCs). In this case, (12.0 x 100) / (100 + 8) = 1200 / 108 = 11.1 x 10^9/L.

Question 129: Hyaline casts in urine are composed mainly of:

Fatty droplets
Tamm-Horsfall protein (Correct answer)
Hemoglobin
White blood cells

Correct answer: Tamm-Horsfall protein

Hyaline casts are formed from Tamm-Horsfall mucoprotein secreted by renal tubular cells and can be present in low numbers in normal urine.

Question 130: What type of extinguisher is used for metal fires?

Class D dry chemical (Correct answer)
Carbon dioxide
A-B-C dry chemical
Water

Correct answer: Class D dry chemical

Explanation: Class D dry chemical extinguishers are specifically designed for metal fires, such as fires involving combustible metals like magnesium, sodium, titanium, or potassium. These extinguishers contain a dry powder agent that effectively smothers and cools the fire, preventing re-ignition and minimizing the risk of explosions.

Question 131: Which of the following staining problems results from the omission of 1% periodic acid solution in the Jones Methenamine silver technique?

Increased non-specific staining will occur
Failure to stain the basement membrane (Correct answer)
Over-impregnation of basement membrane
Nuclei will take up silver stain

Correct answer: Failure to stain the basement membrane

Explanation: The Jones Methenamine silver technique is used to visualize basement membranes in tissue sections. Omitting the 1% periodic acid solution in this technique prevents oxidation of the methenamine silver, resulting in a failure to stain the basement membrane.

Question 132: Which technique is used to detect RNA viruses such as HIV or Hepatitis C virus by molecular methods?

Reverse transcriptase PCR (RT-PCR) (Correct answer)
Pulsed-field gel electrophoresis
Loop-mediated isothermal amplification
Southern blotting

Correct answer: Reverse transcriptase PCR (RT-PCR)

RT-PCR uses reverse transcriptase to first convert the viral RNA into complementary DNA (cDNA), which is then amplified by standard PCR to enable detection of RNA-based targets.

Question 133: Where should a tissue specimen for the frozen section be sent?

Cytology
Chemistry
Microbiology
Histology (Correct answer)

Correct answer: Histology

Explanation: Tissue specimens for frozen section analysis are typically sent to the histology department. Frozen section analysis involves the rapid processing of tissue specimens for immediate examination by a pathologist, often during surgery, to guide surgical decision-making. Histology technicians prepare frozen sections for examination using specialized techniques, making histology the appropriate department for handling such specimens.

Question 134: A physician is evaluating a patient for Cushing's syndrome. Which of the following initial screening tests would be most appropriate to order?

Random serum cortisol
Serum ACTH
High-dose dexamethasone suppression test
24-hour urinary free cortisol (Correct answer)

Correct answer: 24-hour urinary free cortisol

The recommended initial screening tests for Cushing's syndrome include the 24-hour urinary free cortisol, late-night salivary cortisol, and the low-dose dexamethasone suppression test. A 24-hour urinary free cortisol measurement reflects the cortisol production over a full day, overcoming the issue of diurnal variation that makes a random serum cortisol unreliable. High-dose suppression tests and ACTH levels are typically used later to determine the cause of Cushing's syndrome, not for initial screening.

Question 135: Bilirubin in urine is detected by the reagent strip and indicates:

Liver disease or bile duct obstruction (Correct answer)
Increased renal filtration of urea
Hemolytic anemia only
Urinary tract infection

Correct answer: Liver disease or bile duct obstruction

Bilirubinuria results from elevated conjugated (direct) bilirubin in the blood, which is filtered by the kidney in liver disease or obstructive jaundice.

Question 136: According to Canadian Standards Association (CSA) Z902 standards, what is the correct storage temperature range for Platelet concentrates?

1 to 6°C
37 ± 1°C
20 to 24°C (Correct answer)
-18°C or colder

Correct answer: 20 to 24°C

CSA Z902 standards require that platelet components be stored at a controlled room temperature of 20 to 24°C with continuous gentle agitation to maintain their viability and function. Storing them at refrigerated temperatures (1 to 6°C) causes irreversible activation and loss of function.

Question 137: A newborn screening test for congenital adrenal hyperplasia (CAH) is positive. Which analyte is typically measured and expected to be significantly elevated in the most common form of CAH, 21-hydroxylase deficiency?

17-hydroxyprogesterone (Correct answer)
Androstenedione
Cortisol
Deoxycorticosterone

Correct answer: 17-hydroxyprogesterone

In 21-hydroxylase deficiency, the most common cause of CAH, the enzyme needed to convert 17-hydroxyprogesterone to 11-deoxycortisol (a precursor to cortisol) is deficient. This block in the steroid synthesis pathway leads to the accumulation of 17-hydroxyprogesterone, which is then shunted towards androgen production. Therefore, a markedly elevated level of 17-hydroxyprogesterone is the key diagnostic finding.

Question 138: A patient presents with a microcytic anemia. The CBC results are as follows: HGB 105 g/L, MCV 65 fL, RBC 5.5 x 10^12/L, RDW 14.0%. Serum ferritin is normal. Which of the following conditions is most likely?

Beta-thalassemia trait (Correct answer)
Anemia of chronic disease
Iron deficiency anemia
Sideroblastic anemia

Correct answer: Beta-thalassemia trait

In beta-thalassemia trait, there is a defect in beta-globin chain production, leading to small (low MCV) and poorly hemoglobinized red cells. The bone marrow compensates by increasing the production of RBCs, resulting in a characteristically high or normal RBC count relative to the hemoglobin level. Iron deficiency anemia also presents with microcytosis, but typically the RBC count is decreased, and the RDW is often elevated. Normal ferritin rules out iron deficiency.

Question 139: Amniotic fluid bilirubin (delta OD450) measured by spectrophotometry is used to assess:

Severity of fetal hemolytic disease (Correct answer)
Fetal lung maturity
Maternal liver function
Risk of gestational diabetes

Correct answer: Severity of fetal hemolytic disease

Elevated bilirubin in amniotic fluid indicates fetal hemolysis and is measured spectrophotometrically at 450 nm to assess severity of hemolytic disease of the newborn.

CSMLS MLT Certification

The CSMLS certification exam validates entry-level competency for Medical Laboratory Technologists in Canada, covering clinical chemistry, hematology, microbiology, transfusion science, and more.

210

Questions

210 min

Time Limit

65%

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