A patient with suspected renal disease has the following results: serum creatinine 3.2 mg/dL, BUN 48 mg/dL, BUN:creatinine ratio 15:1. Which interpretation is MOST accurate?
- A Pre-renal azotemia (BUN:creatinine >20:1 required)
- B Intrinsic renal disease (ratio 10–20:1 suggests parenchymal damage) ✓
- C Post-renal obstruction
- D Protein malnutrition causing low BUN
Correct answer: B. Intrinsic renal disease (ratio 10–20:1 suggests parenchymal damage)
Explanation
A BUN:creatinine ratio of 10–20:1 suggests intrinsic renal disease (acute tubular necrosis, glomerulonephritis) where both markers rise proportionally. Pre-renal azotemia gives ratio >20:1 because tubular reabsorption of urea is disproportionately high due to reduced GFR. Post-renal obstruction initially causes BUN:creatinine >20:1 as well. The ratio of 15:1 here points to intrinsic renal pathology.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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