Mixed Deck — All Medical Laboratory Technician Exam Topics Flashcards
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Read the first 20 Mixed Deck — All Medical Laboratory Technician Exam Topics flashcards as text
A urine reagent strip is positive for blood, but subsequent microscopic examination reveals no red blood cells. Which of the following is the most likely cause for this discrepancy?
Answer: Presence of myoglobin
The blood pad on the reagent strip detects the peroxidase-like activity of the heme portion of hemoglobin and myoglobin. In cases of rhabdomyolysis (muscle breakdown), myoglobin is released and filtered by the kidneys, causing a positive reagent strip result for blood. However, since there are no intact red blood cells, the microscopic exam will be negative.
Mycotic keratitis is most likely linked to a Fusarium species. A skin infection that commonly affects the feet and causes scaling and itching is called tinea pedis and is caused by the dermatophyte Trichophyton rubrum. Scedosporium apiospermum is commonly associated with sinusitis. Otitis externa is typically brought on by Aspergillus niger, and sinusitis may also be a side effect. Which of the following species or organisms is the most likely to be the cause of mycotic keratitis (fungal eye infection)?
Answer: Fusarium species
Fusarium species are well-established and common causes of mycotic keratitis, which is a fungal infection of the cornea. These fungi are ubiquitous in the environment and can cause infections, particularly after ocular trauma or contact lens use. The other options are associated with different types of fungal infections, as described in the question's preamble.
What is the principle behind the prothrombin time (PT) test?
Answer: Tissue factor activates the extrinsic pathway in recalcified plasma
The PT test measures the extrinsic and common pathways by adding tissue thromboplastin (tissue factor) and calcium to citrated plasma and timing clot formation.
Which immunoglobulin class is produced first during a primary immune response and is the most efficient activator of the classical complement pathway on a per-molecule basis?
Answer: IgM
IgM is the first antibody class secreted following initial antigen exposure. Its pentameric structure provides ten antigen-binding sites and multiple Fc regions that very efficiently fix complement via the classical pathway, even with a single molecule bound to antigen.
Which of the following best describes the mechanism of action of monoclonal antibodies used in immunoassays?
Answer: They are derived from a single B cell clone and bind one epitope
Monoclonal antibodies are produced by hybridomas derived from a single B cell clone and bind a single specific epitope with high specificity.
Which tube color is used for serum chemistry testing because it contains a clot activator and gel separator?
Answer: Gold/SST
Gold or SST (serum separator tube) tubes contain a clot activator and gel separator that isolates serum after centrifugation for chemistry testing.
Which enzyme is essential for the PCR amplification process?
Answer: Taq polymerase
Taq polymerase, derived from Thermus aquaticus, is a heat-stable DNA polymerase that can withstand the high temperatures used in PCR cycling.
Which quality control measure is most important in a molecular diagnostics laboratory to prevent false-positive results?
Answer: Strict physical separation of pre- and post-amplification areas
Physical separation of pre-amplification (specimen prep and PCR setup) from post-amplification (detection) areas prevents amplicon contamination, the primary cause of false-positive PCR results.
A patient with a known IgA deficiency requires a transfusion of packed red blood cells. To prevent a potential anaphylactic transfusion reaction, which modification should be performed on the blood product?
Answer: Washing
Washing red blood cells with sterile saline removes the majority of the plasma, which contains proteins like IgA. In an IgA-deficient patient who has developed anti-IgA antibodies, transfusing plasma-containing products can trigger a severe anaphylactic reaction. Irradiation prevents transfusion-associated graft-versus-host disease, and leukoreduction minimizes febrile reactions and CMV transmission, but neither process removes plasma proteins.
Which urine chemical test principle relies on the double indicator method to detect pH?
Answer: Reagent strip pH pad using methyl red and bromothymol blue
The reagent strip pH pad uses the double indicator system of methyl red and bromothymol blue to cover pH ranges from 5 to 9.
A medical laboratory technician is performing a differential on a Wright-stained peripheral blood smear. They identify red blood cell inclusions that are small, irregular, basophilic granules clustered near the periphery of the cell. A Prussian blue stain confirms the presence of iron. What are these inclusions?
Answer: Pappenheimer bodies
Pappenheimer bodies are abnormal granules of iron, visible as basophilic inclusions on a Wright stain. [22, 30] Their presence is confirmed with a special iron stain like Prussian blue. [24] Howell-Jolly bodies are DNA remnants and are typically single, round, and dense. [24, 28] Basophilic stippling consists of precipitated ribosomes and appears as fine or coarse granules distributed throughout the cell. Cabot rings are rare, thread-like inclusions thought to be remnants of the mitotic spindle.
The temperature is 20 degrees Celsius. Convert it to Fahrenheit.
Answer: 68 degrees F
To convert Celsius to Fahrenheit, the formula F = (C * 9/5) + 32 is used. For 20 degrees Celsius, the calculation is (20 * 9/5) + 32. This equals (36) + 32, which results in 68 degrees Fahrenheit.
To prevent alloimmunization to leukocyte antigens in chronically transfused patients, which blood product modification is most effective?
Answer: Leukoreduction
Leukoreduction is the process of removing white blood cells (leukocytes) from a blood component. This is the most effective method for reducing the risk of febrile non-hemolytic transfusion reactions and alloimmunization to HLA antigens, which are present on leukocytes. Irradiation prevents transfusion-associated graft-versus-host disease, while washing removes plasma proteins to prevent allergic reactions.
A urine specimen tested by dipstick shows a positive result for blood but microscopic examination reveals no red blood cells. Which condition best explains this discrepancy?
Answer: Myoglobinuria from rhabdomyolysis
Dipstick blood reagent pads react with hemoglobin AND myoglobin due to their shared peroxidase-like activity. Myoglobinuria (from muscle breakdown) produces a positive dipstick without intact RBCs on microscopy, distinguishing it from true hematuria.
A synovial fluid aspirate from a patient with acute joint pain is examined using compensated polarized light microscopy. The technologist observes strongly birefringent, needle-shaped crystals that appear yellow when aligned parallel to the slow axis of the compensator. These findings are characteristic of:
Answer: Monosodium urate (MSU) crystals
Monosodium urate (MSU) crystals are characteristically needle-shaped and exhibit strong negative birefringence. Under a compensated polarizing microscope, they appear yellow when their long axis is parallel to the slow axis of the red compensator, which is a classic diagnostic finding for gout.
In a Levey-Jennings chart, which Westgard rule flags a run when one control value exceeds the mean by more than 3 standard deviations?
Answer: 1-3s
The 1-3s Westgard rule is a rejection rule triggered when a single control measurement exceeds ±3 SD from the mean.
A patient's CBC reveals an MCV of 110 fL and oval macrocytes on the peripheral smear. Which nutrient deficiency is most likely responsible?
Answer: Vitamin B12 or folate
Oval macrocytes with elevated MCV are characteristic of megaloblastic anemia caused by vitamin B12 or folate deficiency.
Which molecular technique is used to detect RNA viruses such as HIV or SARS-CoV-2?
Answer: Reverse transcriptase PCR (RT-PCR)
RT-PCR first converts RNA into complementary DNA (cDNA) using reverse transcriptase before PCR amplification, making it suitable for RNA virus detection.
Which of the following is the BEST indicator that a pipette is in need of recalibration?
Answer: QC results show a sudden positive shift across multiple analytes
A sudden positive shift in multiple analytes often points to a volumetric error such as a pipette delivering too much sample.
A patient's antibody screen is positive. The antibody identification panel shows reactivity with all panel cells, and the auto-control is also positive. All reactions are occurring at the AHG phase. Which of the following is the MOST likely cause of these results?
Answer: A warm autoantibody
A warm autoantibody will react with the patient's own red cells (positive auto-control) and all reagent red cells used in the panel because they all possess the common antigens the autoantibody is directed against. The reactions are typically observed at the AHG (37°C) phase. A cold autoantibody typically reacts at room temperature or colder. Multiple alloantibodies would likely show a varying pattern of reactivity, and the auto-control would be negative. An antibody to a high-prevalence antigen would cause reactivity with all panel cells, but the auto-control would be negative.