A patient with chronic renal failure has serum creatinine 8 mg/dL, BUN 80 mg/dL, and a BUN:creatinine ratio of 10:1. This ratio is MORE LIKELY caused by:
- A Prerenal azotemia from dehydration
- B Intrinsic renal disease with proportional reduction in GFR ✓
- C Post-renal obstruction with acute-on-chronic kidney disease
- D High protein diet in a patient with normal renal function
Correct answer: B. Intrinsic renal disease with proportional reduction in GFR
Explanation
A BUN:creatinine ratio of 10:1 is the normal physiological ratio, indicating proportional retention of both nitrogenous wastes in intrinsic renal disease. Prerenal azotemia disproportionately raises BUN (ratio >20:1) because concentrated tubular fluid allows more urea reabsorption alongside water, while creatinine reabsorption is minimal. Post-renal obstruction can produce ratios >20:1 acutely. A normal ratio in the setting of elevated absolute values points to symmetric GFR reduction from intrinsic disease.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
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Written and medically reviewed by the StethoPrep medical team.