NAC OSCE Diagnostic Investigations & Data Interpretation

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?

Accepted Answer

Vitamin B12 deficiency

Answer

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?

Accepted Answer

SIADH

Answer

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?

Accepted Answer

Malignancy

Answer

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?

Accepted Answer

Magnesium

Answer

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?

Accepted Answer

30 mEq/L

Answer

Anion gap = Na − (Cl + HCO3) = 138 − (98 + 10) = 30 mEq/L, indicating a high anion gap metabolic acidosis consistent with diabetic ketoacidosis.

NAC OSCE Practice Test

NAC OSCE Practice Test

NAC OSCE Diagnostic Investigations & Data Interpretation