AOA Clinical Diagnosis and Laboratory Medicine 1 — Questions and Answers
Question 1: A 55-year-old man presents with fatigue, pallor, and a mean corpuscular volume (MCV) of 110 fL. Which finding would best confirm megaloblastic anemia?
- Hypersegmented neutrophils on peripheral smear (Correct answer)
- Target cells on peripheral smear
- Elevated serum ferritin
- Decreased reticulocyte count
Correct answer: Hypersegmented neutrophils on peripheral smear
Hypersegmented neutrophils (≥5 lobes) on peripheral smear are a hallmark of megaloblastic anemia due to B12 or folate deficiency.
Question 2: Which laboratory finding is most characteristic of disseminated intravascular coagulation (DIC)?
- Elevated fibrinogen with normal PT
- Elevated D-dimer with prolonged PT and PTT (Correct answer)
- Isolated thrombocytopenia with normal PT
- Decreased D-dimer with elevated fibrinogen
Correct answer: Elevated D-dimer with prolonged PT and PTT
DIC is characterized by elevated D-dimer (reflecting fibrinolysis), prolonged PT/PTT, and decreased fibrinogen due to widespread coagulation factor consumption.
Question 3: A patient with suspected myocardial infarction presents 6 hours after symptom onset. Which biomarker is most sensitive and specific at this time point?
- Myoglobin
- CK-MB
- Troponin I (Correct answer)
- LDH
Correct answer: Troponin I
Troponin I remains elevated for 7–10 days and is the most sensitive and specific cardiac biomarker from 4–6 hours after MI onset.
Question 4: An anion gap of 22 mEq/L is found in a patient with altered mental status. Which condition is the LEAST likely cause of this elevated anion gap?
- Diabetic ketoacidosis
- Lactic acidosis
- Hyperchloremic metabolic acidosis (Correct answer)
- Uremia
Correct answer: Hyperchloremic metabolic acidosis
Hyperchloremic metabolic acidosis (e.g., from diarrhea or RTA) is a normal anion gap acidosis, not an elevated anion gap acidosis.
Question 5: Which test is considered the gold standard for diagnosing iron deficiency anemia?
- Serum ferritin
- Bone marrow iron staining (Correct answer)
- Serum iron level
- Total iron-binding capacity (TIBC)
Correct answer: Bone marrow iron staining
Bone marrow iron staining directly visualizes iron stores and is the definitive gold standard, though serum ferritin is the most practical first-line test.
Question 6: A 30-year-old woman has a serum calcium of 11.5 mg/dL. PTH is elevated. What is the most likely diagnosis?
- Malignancy-associated hypercalcemia
- Primary hyperparathyroidism (Correct answer)
- Milk-alkali syndrome
- Vitamin D toxicity
Correct answer: Primary hyperparathyroidism
Elevated PTH with hypercalcemia is diagnostic of primary hyperparathyroidism; malignancy suppresses PTH via PTHrP production.
Question 7: Which urinalysis finding is most consistent with a diagnosis of nephrotic syndrome?
- WBC casts
- RBC casts
- Fatty casts and oval fat bodies (Correct answer)
- Granular muddy-brown casts
Correct answer: Fatty casts and oval fat bodies
Fatty casts and oval fat bodies in urine are characteristic of nephrotic syndrome due to massive proteinuria and lipiduria.
AOA Clinical Diagnosis and Laboratory Medicine 1
A 55-year-old man presents with fatigue, pallor, and a mean corpuscular volume (MCV) of 110 fL.
Which finding would best confirm megaloblastic anemia?