A serum creatinine of 6.0 mg/dL would most likely be accompanied by which BUN result?

A serum creatinine of 6.0 mg/dL would most likely be accompanied by which BUN result?

• A. 6 mg/dL
• B. 20 mg/dL
• C. 35 mg/dL
• D. 70 mg/dL

Answer: (D)

The main idea is how kidney function affects waste products in the blood. When the glomerular filtration rate drops, both creatinine and BUN rise, but their relative rise is usually proportional, giving a BUN to creatinine ratio in the roughly normal range of about 10–20:1 for significant kidney dysfunction. A creatinine of 6 mg/dL signals severe renal impairment, so you’d expect a relatively high BUN as well. Among the options, a BUN of 70 mg/dL yields a BUN/creatinine ratio around 11–12, which fits that pattern and typical physiology. The other values would produce ratios that are unusually low for this level of creatinine, making them less consistent with marked renal failure.

The main idea is how kidney function affects waste products in the blood. When the glomerular filtration rate drops, both creatinine and BUN rise, but their relative rise is usually proportional, giving a BUN to creatinine ratio in the roughly normal range of about 10–20:1 for significant kidney dysfunction. A creatinine of 6 mg/dL signals severe renal impairment, so you’d expect a relatively high BUN as well. Among the options, a BUN of 70 mg/dL yields a BUN/creatinine ratio around 11–12, which fits that pattern and typical physiology. The other values would produce ratios that are unusually low for this level of creatinine, making them less consistent with marked renal failure.