skip to main content

Prerenal acute kidney injury — USMLE Step 2 CK MCQ

Instant feedback + full explanation. One question, done properly.

HardInternal MedicinePrerenal acute kidney injuryUSMLE Step 2 CK

A 74-year-old taking furosemide has 3 days of vomiting and orthostatic dizziness. Creatinine rises from 1.0 to 3.2 mg/dL. Urine sodium is 38 mEq/L, urine urea nitrogen is 300 mg/dL, plasma urea nitrogen is 50 mg/dL, and urine creatinine is 80 mg/dL. Urinalysis is bland. Which process best explains the acute kidney injury?

Educational content. Not a substitute for clinical judgement or local policy.

Reveal the answer and explanation

Correct answer: C — Volume-responsive prerenal azotemia despite diuretic exposure

Explanation lettering: C = shown as A · E = shown as B · D = shown as C · A = shown as D · B = shown as E

D is correct: because loop diuretics confound fractional sodium excretion, fractional excretion of urea is more useful here: (300 × 3.2)/(50 × 80) × 100 = 24%, below 35%, supporting prerenal physiology with vomiting, orthostasis, and bland sediment. A usually produces granular casts and a higher fractional urea excretion. B commonly causes pyuria or white-cell casts. C should cause hematuria and proteinuria. E requires obstructive evidence and is not explained by these volume-loss findings.

Reference: KDIGO acute kidney injury guideline appendices. https://kdigo.org/wp-content/uploads/2016/10/KDIGO-AKI-Suppl-Appendices-A-F_March2012.pdf