MLPAO Clinical Chemistry Laboratory Practice 2 — Questions and Answers
Question 1: What is the purpose of the Levey-Jennings chart in quality control?
- To calculate reference ranges
- To plot QC results over time and visually detect trends, shifts, and outliers (Correct answer)
- To compare patient results between laboratories
- To determine the analytical measurement range
Correct answer: To plot QC results over time and visually detect trends, shifts, and outliers
A Levey-Jennings chart plots QC values over time with the mean and standard deviation limits displayed. This visual tool allows laboratory professionals to identify patterns such as shifts (sudden change in mean), trends (gradual change), and outliers that indicate analytical problems.
Question 2: Which type of error is characterized by results that are consistently higher or lower than the true value?
- Random error
- Systematic error (bias) (Correct answer)
- Preanalytical error
- Gross error
Correct answer: Systematic error (bias)
Systematic error (bias) produces results that are consistently displaced in one direction from the true value. It can be constant (same magnitude regardless of concentration) or proportional (error changes with concentration). Causes include calibration errors, reagent deterioration, and matrix effects.
Question 3: What is the clinical significance of measuring serum haptoglobin?
- Detecting iron overload
- Confirming intravascular hemolysis (Correct answer)
- Monitoring liver synthetic function
- Assessing complement activation
Correct answer: Confirming intravascular hemolysis
Serum haptoglobin binds free hemoglobin released during intravascular hemolysis. The haptoglobin-hemoglobin complex is cleared by the reticuloendothelial system, resulting in decreased or absent serum haptoglobin. It is a sensitive marker for intravascular hemolysis when combined with elevated LDH and indirect bilirubin.
Question 4: Which condition would cause an elevated anion gap metabolic acidosis?
- Diarrhea
- Renal tubular acidosis
- Diabetic ketoacidosis (Correct answer)
- Normal saline infusion
Correct answer: Diabetic ketoacidosis
Diabetic ketoacidosis (DKA) causes elevated anion gap metabolic acidosis due to accumulation of ketoacids (acetoacetate and beta-hydroxybutyrate). The mnemonic MUDPILES helps remember causes: Methanol, Uremia, DKA, Propylene glycol, Isoniazid/Iron, Lactic acidosis, Ethylene glycol, Salicylates.
Question 5: What is the role of internal standard in mass spectrometry-based clinical chemistry methods?
- To calibrate the mass spectrometer detector
- To compensate for matrix effects and variations in ionization efficiency (Correct answer)
- To verify the purity of solvents
- To establish the mobile phase gradient
Correct answer: To compensate for matrix effects and variations in ionization efficiency
Internal standards (typically isotope-labeled analogs of the target analyte) are added to specimens before extraction to compensate for variations in sample preparation, matrix effects, and ionization efficiency. The ratio of analyte signal to internal standard signal provides accurate quantitation.
Question 6: Which condition is associated with elevated serum phosphate and decreased calcium?
- Primary hyperparathyroidism
- Chronic kidney disease (Correct answer)
- Vitamin D toxicity
- Thiazide diuretic use
Correct answer: Chronic kidney disease
Chronic kidney disease causes hyperphosphatemia due to decreased renal phosphate excretion and hypocalcemia due to decreased vitamin D activation (1,25-dihydroxyvitamin D) by the diseased kidneys. This reciprocal relationship drives secondary hyperparathyroidism in CKD patients.
MLPAO Clinical Chemistry Laboratory Practice 2
What is the purpose of the Levey-Jennings chart in quality control?