AOA Clinical Diagnosis and Laboratory Medicine 2 — Questions and Answers
Question 1: Which interpretation of an arterial blood gas — pH 7.28, PaCO2 55 mmHg, HCO3 24 mEq/L — is correct?
- Metabolic acidosis
- Respiratory alkalosis
- Respiratory acidosis (Correct answer)
- Mixed metabolic and respiratory acidosis
Correct answer: Respiratory acidosis
Low pH with elevated PaCO2 and normal bicarbonate indicates an acute respiratory acidosis without metabolic compensation.
Question 2: A patient has an AST/ALT ratio greater than 2:1 with elevated GGT and elevated MCV. What is the most likely diagnosis?
- Viral hepatitis B
- Alcoholic liver disease (Correct answer)
- Autoimmune hepatitis
- Non-alcoholic fatty liver disease
Correct answer: Alcoholic liver disease
An AST:ALT ratio >2:1, elevated GGT, and macrocytosis (elevated MCV) form a classic triad strongly suggesting alcoholic liver disease.
Question 3: In interpreting a Coombs test for hemolytic anemia, a positive direct antiglobulin test (DAT) indicates:
- Antibodies in the serum against foreign red cells
- Antibodies bound directly to the patient's red blood cells (Correct answer)
- Complement activation only in plasma
- Alloantibody production after transfusion
Correct answer: Antibodies bound directly to the patient's red blood cells
The direct Coombs (DAT) detects antibodies or complement already bound to the patient's own red blood cells, indicating autoimmune or drug-induced hemolysis.
Question 4: A 45-year-old with dyslipidemia has an LDL of 190 mg/dL despite lifestyle changes. According to ACC/AHA guidelines, which lab result would most support initiating high-intensity statin therapy?
- HDL of 60 mg/dL
- Triglycerides of 150 mg/dL
- LDL ≥ 190 mg/dL on two separate measurements (Correct answer)
- CRP of 1.0 mg/L
Correct answer: LDL ≥ 190 mg/dL on two separate measurements
ACC/AHA guidelines recommend high-intensity statin therapy for LDL ≥190 mg/dL, regardless of 10-year cardiovascular risk score.
Question 5: Which thyroid function test pattern is consistent with subclinical hypothyroidism?
- Low TSH, low free T4
- Elevated TSH, normal free T4 (Correct answer)
- Normal TSH, low free T4
- Elevated TSH, elevated free T4
Correct answer: Elevated TSH, normal free T4
Subclinical hypothyroidism is defined by elevated TSH with a normal free T4, indicating early thyroid insufficiency without overt hormonal deficiency.
Question 6: A patient has a serum sodium of 125 mEq/L with low urine osmolality (< 100 mOsm/kg) and low urine sodium (< 20 mEq/L). What is the most likely cause?
- SIADH
- Primary polydipsia (Correct answer)
- Adrenal insufficiency
- Hypothyroidism
Correct answer: Primary polydipsia
Dilute urine (low urine osmolality) with low urine sodium in the setting of hyponatremia is classic for primary polydipsia, where excess free water suppresses ADH.
Question 7: Which finding on peripheral blood smear is most consistent with thrombotic thrombocytopenic purpura (TTP)?
- Spherocytes
- Schistocytes (helmet cells) (Correct answer)
- Hypersegmented neutrophils
- Teardrop cells
Correct answer: Schistocytes (helmet cells)
Schistocytes (fragmented red cells/helmet cells) result from mechanical destruction of RBCs by platelet thrombi in microvasculature, hallmark of TTP.
AOA Clinical Diagnosis and Laboratory Medicine 2
Which interpretation of an arterial blood gas — pH 7.28, PaCO2 55 mmHg, HCO3 24 mEq/L — is correct?