Which laboratory value is most indicative of acute renal impairment?

• A. Creatinine 0.9 mg/dL
• B. BUN 18 mg/dL
• C. BUN 60 mg/dL
• D. Potassium 4.2 mEq/L

Answer: (C)

Acute renal impairment shows up as a sudden buildup of waste products the kidneys can’t clear. BUN reflects such waste accumulation and rises when kidney clearance falls. A BUN of 60 mg/dL is markedly elevated, signaling azotemia from reduced renal function. In contrast, creatinine at 0.9 mg/dL is within the normal range and, by itself, doesn’t indicate impairment here, and potassium at 4.2 mEq/L is also normal. So the markedly high BUN is the clearest indicator of acute renal impairment among these values.