PEBC Diagnostic Procedures 5 — Questions and Answers
Question 1: A patient on lithium therapy has a serum lithium level of 1.8 mmol/L. The therapeutic range is 0.6–1.2 mmol/L. Which symptom is most consistent with lithium toxicity?
- Polyuria and polydipsia
- Fine hand tremor
- Coarse tremor, ataxia, and confusion (Correct answer)
- Weight gain and hypothyroidism
Correct answer: Coarse tremor, ataxia, and confusion
Serum lithium > 1.5 mmol/L indicates serious toxicity, manifesting as coarse tremor, ataxia, confusion, and in severe cases, seizures or coma.
Question 2: Which test is the gold standard for diagnosing pulmonary embolism?
- D-dimer blood test
- Ventilation-perfusion (V/Q) scan
- CT pulmonary angiography (CTPA) (Correct answer)
- Chest X-ray
Correct answer: CT pulmonary angiography (CTPA)
CT pulmonary angiography is the preferred and gold standard imaging modality for diagnosing pulmonary embolism due to its high sensitivity and specificity.
Question 3: A patient's stool culture is positive for Clostridioides difficile toxin. Which test characteristic makes the PCR assay preferred over enzyme immunoassay (EIA) for toxin detection?
- Lower cost per test
- Higher sensitivity for detecting toxin genes (Correct answer)
- Shorter turnaround time only
- Ability to detect all Gram-positive bacteria
Correct answer: Higher sensitivity for detecting toxin genes
PCR-based testing detects the toxin gene with higher sensitivity than EIA toxin detection, reducing the rate of false-negative results in C. difficile infection diagnosis.
Question 4: A pharmacist is counselling a patient about their INR result of 1.1 while on warfarin for atrial fibrillation (target INR 2.0–3.0). Which is the most likely cause of a subtherapeutic INR?
- Increased dietary vitamin K intake (Correct answer)
- Concurrent use of fluconazole
- Recent antibiotic use eliminating gut flora
- Vitamin C supplementation
Correct answer: Increased dietary vitamin K intake
Vitamin K competes with warfarin's mechanism, and a high dietary intake of vitamin K–rich foods reduces warfarin's anticoagulant effect, leading to a subtherapeutic INR.
Question 5: A patient is referred for a bone mineral density (BMD) test. Their T-score at the femoral neck is −2.6. How should the pharmacist interpret this result?
- Normal bone density
- Osteopenia (low bone mass)
- Osteoporosis (Correct answer)
- Severe osteoporosis with fracture
Correct answer: Osteoporosis
A T-score of −2.5 or lower is diagnostic of osteoporosis per WHO criteria; a T-score of −2.6 meets this threshold.
Question 6: Which laboratory result is a contraindication to initiating metformin therapy?
- eGFR 55 mL/min/1.73m²
- eGFR 28 mL/min/1.73m² (Correct answer)
- Fasting glucose 9.2 mmol/L
- HbA1c 8.5%
Correct answer: eGFR 28 mL/min/1.73m²
Metformin is contraindicated when eGFR < 30 mL/min/1.73m² due to the risk of lactic acidosis from drug accumulation; caution is advised at eGFR 30–45.
Question 7: A neonatal screen returns positive for phenylketonuria (PKU). Which confirmatory diagnostic test is required?
- Urine amino acid chromatography alone
- Serum phenylalanine and tetrahydrobiopterin (BH4) loading test (Correct answer)
- Liver biopsy for phenylalanine hydroxylase activity
- Genetic panel for PKU mutations only
Correct answer: Serum phenylalanine and tetrahydrobiopterin (BH4) loading test
Confirmatory diagnosis of PKU requires elevated serum phenylalanine levels and a BH4 loading test to differentiate classic PKU from BH4-responsive forms and BH4 deficiencies.
PEBC Diagnostic Procedures 5
A patient on lithium therapy has a serum lithium level of 1.8 mmol/L.
The therapeutic range is 0.6–1.2 mmol/L.
Which symptom is most consistent with lithium toxicity?