BUN vs creatinine — what's the difference?
Both reflect kidney function, but the ratio differentiates causes. BUN/creatinine > 20:1 suggests pre-renal causes (dehydration, GI bleeding); <10:1 suggests intrinsic renal or low protein intake.
Full answer
BUN and creatinine are both markers of kidney function but respond differently to non-renal influences. BUN rises with high protein intake, dehydration, GI bleeding, and catabolic states; creatinine is more steady, reflecting muscle mass and renal filtration. The BUN-to-creatinine ratio differentiates causes of elevation. Ratio >20:1 suggests pre-renal causes (dehydration, GI bleed, high protein); ratio 10-20:1 is typical of intrinsic renal disease; ratio <10:1 suggests low muscle mass, low protein intake, or rhabdomyolysis. Provider review interprets both with eGFR and clinical context.
Educational. Not a substitute for individualized provider review.
- Creatinine — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29