CSMLS Clinical Chemistry Procedures Questions and Answers — Questions and Answers
Question 1: 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 acidosis
- Respiratory alkalosis
- Metabolic 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 2: 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?
- Report patient results and document the QC deviation.
- Recalibrate the instrument immediately.
- Repeat the control on the same vial. (Correct answer)
- Open a new vial of control and repeat the measurement.
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 3: 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 4: A patient sample for electrolyte analysis is noted to be severely hemolyzed. Which analyte would be most significantly falsely elevated?
- Sodium (Na+)
- Potassium (K+) (Correct answer)
- Chloride (Cl-)
- 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 5: 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:
- Normal glucose tolerance
- Impaired fasting glucose (IFG)
- Impaired glucose tolerance (IGT)
- Diabetes mellitus (Correct answer)
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 6: What is the principle of the Jaffe reaction for measuring creatinine?
- Creatinine reacts with picric acid in an alkaline solution to form a red-orange complex. (Correct answer)
- An enzymatic reaction using creatininase produces a colored product measured spectrophotometrically.
- Creatinine is measured directly using an ion-selective electrode.
- Urease converts urea to ammonia, and the resulting change in conductivity is measured.
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.
CSMLS Clinical Chemistry Procedures Questions and Answers
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?