Which set of laboratory results most accurately reflects severe renal disease?

• A. Serum creatinine 3.7 mg/dL; creatinine clearance 44 mL/min; BUN 88 mg/dL
• B. Serum creatinine 1.0 mg/dL; creatinine clearance 110 mL/min; BUN 17 mg/dL
• C. Serum creatinine 2.0 mg/dL; creatinine clearance 120 mL/min; BUN 14 mg/dL
• D. Serum creatinine 1.0 mg/dL; creatinine clearance 95 mL/min; BUN 43 mg/dL

Answer: (A)

Kidneys failing to filter waste results in a drop in the filtering rate (GFR) and a buildup of waste products in the blood, shown by elevated creatinine and BUN, along with a reduced creatinine clearance that estimates GFR. The most severe pattern here is when creatinine is very high, clearance is markedly reduced, and BUN is also very high. The set with serum creatinine of 3.7 mg/dL, creatinine clearance of 44 mL/min, and BUN of 88 mg/dL fits this: creatinine is far above normal, clearance is well below normal, and BUN is markedly elevated, all pointing to substantially impaired kidney function.

Other patterns either show preserved filtration (clearance around 95–110 mL/min) or mismatched values that don’t align with severe kidney failure, such as a high BUN with normal creatinine, which can occur with dehydration or other nonrenal factors, or a high creatinine with an unrealistically high clearance, which isn’t consistent with reduced kidney function.