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.
Specialty: Nephrology, Clinical Laboratory
ICD-10: ,