CLS Clinical Chemistry 2 — Questions and Answers
Question 1: Which thyroid function test is considered the most sensitive initial screening test for thyroid disorders?
- Free T4 (FT4)
- Total T3
- Thyroid-stimulating hormone (TSH) (Correct answer)
- Thyroglobulin
Correct answer: Thyroid-stimulating hormone (TSH)
TSH is the most sensitive initial screening test because small changes in thyroid hormone levels trigger large compensatory changes in TSH secretion.
Question 2: A patient has elevated AST and ALT with a De Ritis ratio (AST/ALT) greater than 2:1. This pattern is most consistent with which condition?
- Viral hepatitis
- Alcoholic liver disease (Correct answer)
- Nonalcoholic fatty liver disease
- Biliary obstruction
Correct answer: Alcoholic liver disease
An AST/ALT ratio greater than 2:1 is characteristic of alcoholic liver disease because alcohol and its metabolites selectively damage mitochondria, elevating AST disproportionately.
Question 3: Which analyte is measured to assess pancreatic exocrine function and is elevated in acute pancreatitis?
- Lipase and amylase (Correct answer)
- Alkaline phosphatase and GGT
- Bilirubin and albumin
- Troponin and CK-MB
Correct answer: Lipase and amylase
Lipase and amylase are pancreatic enzymes released into the bloodstream during acute pancreatitis, with lipase being more specific and remaining elevated longer.
Question 4: In a patient with metabolic acidosis, which finding would indicate respiratory compensation?
- Increased PCO2 above 40 mmHg
- Decreased PCO2 below 40 mmHg (Correct answer)
- Increased HCO3- above 26 mEq/L
- Decreased pH below 7.35 with normal PCO2
Correct answer: Decreased PCO2 below 40 mmHg
In metabolic acidosis, the respiratory system compensates by hyperventilating to blow off CO2, resulting in a decreased PCO2.
Question 5: Which protein is measured to assess long-term glycemic control over approximately 2-3 months?
- Fructosamine
- Glycated hemoglobin (HbA1c) (Correct answer)
- C-peptide
- Proinsulin
Correct answer: Glycated hemoglobin (HbA1c)
HbA1c reflects average blood glucose over the preceding 2-3 months, correlating with the lifespan of red blood cells.
Question 6: A serum total bilirubin is 8 mg/dL with direct bilirubin of 6.5 mg/dL. This fractionation pattern is most consistent with which type of jaundice?
- Prehepatic (hemolytic) jaundice
- Intrahepatic jaundice from hepatocellular damage
- Posthepatic (obstructive) jaundice (Correct answer)
- Neonatal physiologic jaundice
Correct answer: Posthepatic (obstructive) jaundice
Elevated direct (conjugated) bilirubin predominating over indirect bilirubin indicates posthepatic obstruction, where conjugated bilirubin cannot be excreted into bile.
Question 7: Which electrolyte abnormality is most likely to cause prolonged QT interval and potentially fatal cardiac arrhythmias?
- Hypernatremia
- Hypomagnesemia (Correct answer)
- Hyperchloremia
- Hyponatremia
Correct answer: Hypomagnesemia
Hypomagnesemia can prolong the QT interval and cause life-threatening ventricular arrhythmias, including torsades de pointes.
CLS Clinical Chemistry 2
Which thyroid function test is considered the most sensitive initial screening test for thyroid disorders?