NAC OSCE Diagnostic Investigations & Data Interpretation 1 — Questions and Answers
Question 1: A 58-year-old woman presents with fatigue and pallor. Labs show Hgb 78 g/L, MCV 112 fL, and hypersegmented neutrophils on peripheral smear. Which of the following is the most likely underlying cause?
- Iron deficiency anemia
- Vitamin B12 deficiency (Correct answer)
- Anemia of chronic disease
- Thalassemia minor
Correct answer: Vitamin B12 deficiency
Macrocytic anemia (MCV >100) with hypersegmented neutrophils is the classic presentation of megaloblastic anemia due to Vitamin B12 or folate deficiency.
Question 2: A 65-year-old man on hydrochlorothiazide has serum Na 118 mEq/L, serum osmolality 258 mOsm/kg, and urine osmolality 580 mOsm/kg. What is the most likely diagnosis?
- Diabetes insipidus
- Psychogenic polydipsia
- SIADH (Correct answer)
- Cerebral salt wasting
Correct answer: SIADH
SIADH presents with hyponatremia, low serum osmolality, and inappropriately concentrated urine (urine osmolality >100 mOsm/kg); thiazides are a common cause.
Question 3: A 72-year-old woman presents with confusion, constipation, and polyuria. Her corrected serum calcium is 3.3 mmol/L. Which is the most likely cause of severe hypercalcemia in this clinical context?
- Primary hyperparathyroidism
- Vitamin D intoxication
- Sarcoidosis
- Malignancy (Correct answer)
Correct answer: Malignancy
Malignancy is the most common cause of severe symptomatic hypercalcemia in hospitalized or acutely ill elderly patients, typically through PTHrP secretion or osteolytic metastases.
Question 4: A 40-year-old with alcohol use disorder presents with weakness and muscle cramps. Labs: K+ 2.8 mEq/L, Mg2+ 0.45 mmol/L (low), PO4 0.6 mmol/L. Which electrolyte deficiency must be corrected first to successfully treat the hypokalemia?
- Potassium
- Magnesium (Correct answer)
- Phosphate
- Calcium
Correct answer: Magnesium
Hypomagnesemia impairs renal potassium conservation and intracellular potassium uptake; potassium replacement will be ineffective until magnesium is corrected.
Question 5: A diabetic patient's ABG shows pH 7.28, pCO2 22 mmHg, HCO3 10 mEq/L; serum Na 138 mEq/L, Cl 98 mEq/L. What is the calculated anion gap?
- 12 mEq/L
- 18 mEq/L
- 30 mEq/L (Correct answer)
- 40 mEq/L
Correct answer: 30 mEq/L
Anion gap = Na − (Cl + HCO3) = 138 − (98 + 10) = 30 mEq/L, indicating a high anion gap metabolic acidosis consistent with diabetic ketoacidosis.
Question 6: A 35-year-old woman presents with fatigue and hair loss. TSH is 12 mU/L (normal 0.4–4.0), free T4 is low, and anti-TPO antibodies are markedly elevated. What is the most likely diagnosis?
- Graves' disease
- De Quervain thyroiditis
- Hashimoto's thyroiditis (Correct answer)
- Central hypothyroidism
Correct answer: Hashimoto's thyroiditis
Hashimoto's thyroiditis is an autoimmune hypothyroidism characterized by elevated TSH, low free T4, and markedly positive anti-thyroid peroxidase (anti-TPO) antibodies.
Question 7: A 50-year-old man presents with chest pain. Troponin I is 0.08 ng/mL (upper reference limit 0.04 ng/mL). ECG shows no ST changes or new LBBB. What is the most appropriate immediate next step?
- Discharge with outpatient cardiology follow-up
- Repeat troponin in 3–6 hours and continue monitoring (Correct answer)
- Immediate coronary angiography
- Administer thrombolytics
Correct answer: Repeat troponin in 3–6 hours and continue monitoring
A mildly elevated troponin without ST elevation requires serial troponin measurements at 3–6 hours to establish a rising or falling pattern consistent with acute myocardial injury (NSTEMI workup).
NAC OSCE Diagnostic Investigations & Data Interpretation 1
A 58-year-old woman presents with fatigue and pallor.
Labs show Hgb 78 g/L, MCV 112 fL, and hypersegmented neutrophils on peripheral smear.
Which of the following is the most likely underlying cause?