A high BUN-to-creatinine ratio is found in overproduction of urea nitrogen or in reduced excretion of urea nitrogen. The ratio is best used only as a rough guide, due to variability in results related to variability in diet and muscle mass.
BUN-to-Creatinine ratio =
= ((serum urea nitrogen in mg/dL) / (serum creatinine in mg/dL))
Interpretation
The normal range for a healthy person on a normal diet is 12-20, with most 12-16.
Ratio
Consider
normal (12 – 20)
• normal renal function
• acute renal failure
• chronic renal failure
elevated (> 20)
• prerenal azotemia;
• postrenal azotemia;
• catabolic state, with reduced muscle mass;
• drug (tetracycline, glucocorticoid) effects;
• impaired renal function with urine reabsorption, for example with ureterocolostomy;
• impaired renal function with excess protein intake/production or with excess tissue breakdown, as may occur with GI bleeding, thyrotoxicosis, infection, Cushing's syndrome, surgery, burns, cachexia, high fever, or high protein diet.
• A ratio > 36 suggests upper GI bleeding.
decreased (< 10)
• renal dialysis
• acute tubular necrosis
• low protein diet or starvation
• syndrome of inappropriate ADH secretion
• pregnancy
• severe liver disease
• inherited hyperammonemia
Limitations:
• A person with low muscle mass or protein malnutrition may have a low serum BUN, and the ratio would be an unreliable indicator of renal status.
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