Medical Laboratory Technician Clinical Chemistry Procedures Questions and Answers — Questions and Answers
Question 1: A patient's blood gas results are as follows: pH = 7.25, pCO2 = 60 mmHg, HCO3- = 24 mEq/L. How would you classify this acid-base disturbance?
- Metabolic Acidosis
- Respiratory Alkalosis
- Metabolic Alkalosis
- Respiratory Acidosis (Correct answer)
Correct answer: Respiratory Acidosis
The pH is below the normal range (7.35-7.45), indicating acidosis. The pCO2 is elevated (normal range 35-45 mmHg), which is the respiratory component. The HCO3- is within the normal range (22-26 mEq/L). Therefore, the primary disturbance is respiratory acidosis, as the high level of CO2 (an acid) is not being compensated for by the kidneys (metabolic component).
Question 2: A physician orders a creatinine clearance test to evaluate a patient's kidney function. The following results are obtained: - Serum creatinine: 1.5 mg/dL - Urine creatinine: 120 mg/dL - Urine volume: 1440 mL/24 hours - Body Surface Area (BSA): 1.73 m² Using the standard formula, what is the calculated creatinine clearance in mL/min?
- 60 mL/min
- 120 mL/min
- 80 mL/min (Correct answer)
- 100 mL/min
Correct answer: 80 mL/min
The formula for creatinine clearance is: (Urine Creatinine x Urine Volume) / (Serum Creatinine x Time in minutes). First, convert the 24-hour urine volume to mL/min: 1440 mL / 1440 min = 1 mL/min. Then, apply the formula: (120 mg/dL * 1 mL/min) / 1.5 mg/dL = 80 mL/min. Since the patient's BSA is the standard 1.73 m², no correction is needed.
Question 3: Which of the following cardiac markers is the most specific for myocardial infarction and remains elevated for the longest duration after the event?
- CK-MB
- Myoglobin
- Troponin I (Correct answer)
- AST
Correct answer: Troponin I
Troponin I is a protein that is highly specific to cardiac muscle. Following a myocardial infarction (heart attack), its levels rise within 3-6 hours, peak at 12-24 hours, and can remain elevated for 7-14 days. CK-MB and myoglobin rise earlier but are less specific and return to normal more quickly. AST is an older, non-specific marker for cardiac damage.
Question 4: A laboratorian performs an ion-selective electrode (ISE) measurement for electrolytes. The technologist notices that the potassium result is critically high, but the patient has no symptoms of hyperkalemia. A visual inspection of the serum shows significant hemolysis. Which of the following is the most likely explanation for the discrepant result?
- Instrument malfunction
- Incorrect sample collection tube was used
- Intracellular potassium was released from lysed red blood cells (Correct answer)
- The patient was not fasting prior to the blood draw
Correct answer: Intracellular potassium was released from lysed red blood cells
Potassium is primarily an intracellular cation. Its concentration inside red blood cells is significantly higher than in the plasma. When hemolysis (rupture of red blood cells) occurs, this intracellular potassium is released into the serum, causing a falsely elevated (pseudohyperkalemia) result that does not reflect the patient's true physiological state.
Question 5: A patient with a history of diabetes has a Hemoglobin A1c (HbA1c) level of 9.0%. This result reflects the patient's average blood glucose level over what period of time?
- The past 24 hours
- The past 7 days
- The past 2-3 months (Correct answer)
- The past 6 months
Correct answer: The past 2-3 months
Hemoglobin A1c is formed when glucose in the blood binds irreversibly to hemoglobin within red blood cells. The level of HbA1c is proportional to the average glucose concentration in the blood. Since the average lifespan of a red blood cell is about 120 days, the HbA1c test provides an integrated picture of blood glucose control over the preceding 2-3 months.
Question 6: In spectrophotometry, the relationship between the absorbance of a solution and the concentration of the analyte in the solution is described by which of the following laws?
- Charles's Law
- Beer's Law (Correct answer)
- Boyle's Law
- Dalton's Law
Correct answer: Beer's Law
Beer's Law (or the Beer-Lambert Law) states that the absorbance of light by a solution is directly proportional to the concentration of the absorbing substance (analyte) and the path length of the light through the solution. This principle is fundamental to quantitative analysis in clinical chemistry using spectrophotometers.
Medical Laboratory Technician Clinical Chemistry Procedures Questions and Answers
A patient's blood gas results are as follows: pH = 7.25, pCO2 = 60 mmHg, HCO3- = 24 mEq/L.
How would you classify this acid-base disturbance?