MLPAO Clinical Chemistry Fundamentals 2 — Questions and Answers
Question 1: In the measurement of serum electrolytes, which technology uses ion-selective electrodes (ISE)?
- Spectrophotometry
- Potentiometry (Correct answer)
- Nephelometry
- Turbidimetry
Correct answer: Potentiometry
Potentiometry is the electrochemical technique that uses ion-selective electrodes to measure electrolyte concentrations. ISE technology measures the electrical potential difference generated across a membrane selective for a specific ion, providing direct measurement of ion activity.
Question 2: What is the clinical significance of an elevated serum amylase level?
- Renal failure
- Acute pancreatitis (Correct answer)
- Congestive heart failure
- Hypothyroidism
Correct answer: Acute pancreatitis
Elevated serum amylase is most commonly associated with acute pancreatitis. Amylase is released from damaged pancreatic acinar cells into the bloodstream. However, amylase can also be elevated in other conditions such as salivary gland disorders and intestinal obstruction.
Question 3: Which specimen type is preferred for most clinical chemistry analyses?
- Whole blood in EDTA
- Serum from a red-top tube (Correct answer)
- Plasma from a heparin tube
- Capillary blood
Correct answer: Serum from a red-top tube
Serum collected in a red-top (no additive) tube or serum separator tube (SST) is preferred for most clinical chemistry analyses. Serum lacks fibrinogen and clotting factors, providing a cleaner matrix that minimizes interference with many analytical methods.
Question 4: What is the Henderson-Hasselbalch equation used to calculate in clinical chemistry?
- Anion gap
- Blood pH from bicarbonate and pCO2 (Correct answer)
- Creatinine clearance
- Osmolal gap
Correct answer: Blood pH from bicarbonate and pCO2
The Henderson-Hasselbalch equation calculates blood pH from the ratio of bicarbonate concentration to dissolved CO2 (pCO2). The equation is pH = pK + log([HCO3-]/[0.03 × pCO2]), and it is fundamental to understanding acid-base physiology.
Question 5: Which condition is characterized by elevated serum bilirubin with a predominantly unconjugated (indirect) fraction?
- Biliary obstruction
- Hemolytic anemia (Correct answer)
- Hepatocellular carcinoma
- Cholestasis
Correct answer: Hemolytic anemia
Hemolytic anemia causes elevated unconjugated (indirect) bilirubin because the excessive breakdown of red blood cells overwhelms the liver's capacity to conjugate bilirubin. In contrast, obstructive and hepatocellular conditions typically elevate conjugated (direct) bilirubin.
Question 6: What does the anion gap calculation help identify?
- Respiratory alkalosis
- Metabolic acidosis etiology (Correct answer)
- Hypernatremia cause
- Renal tubular function
Correct answer: Metabolic acidosis etiology
The anion gap helps differentiate causes of metabolic acidosis. It is calculated as Na+ - (Cl- + HCO3-), with a normal range of approximately 8-12 mmol/L. An elevated anion gap suggests accumulation of unmeasured acids such as lactate, ketoacids, or toxins.
MLPAO Clinical Chemistry Fundamentals 2
In the measurement of serum electrolytes, which technology uses ion-selective electrodes (ISE)?