BUN/Creatinine Ratio Calculator
The BUN/Creatinine ratio is a simple blood test calculation that helps clinicians figure out why kidney function markers are elevated. Enter your BUN and serum creatinine values to calculate the ratio and see what range it falls into.
Both BUN (blood urea nitrogen) and creatinine are waste products filtered by the kidneys, but they behave differently in various clinical scenarios. That difference is what makes the ratio useful.
Normal range: A BUN/Creatinine ratio between 10:1 and 20:1 is considered normal in most adults.
Elevated ratio (> 20:1): This pattern often points to prerenal causes, where something is reducing blood flow to the kidneys before they can filter properly. Common scenarios include:
- Dehydration or volume depletion
- Congestive heart failure with low cardiac output
- GI bleeding (digested blood protein raises BUN)
- High protein diet or catabolic states
- Corticosteroid therapy
Low ratio (< 10:1): A disproportionately low BUN relative to creatinine suggests:
- Intrinsic kidney damage (acute tubular necrosis)
- Liver disease (reduced urea production)
- Low protein intake or malnutrition
- Rhabdomyolysis (massive creatinine release from muscle breakdown)
The ratio is a screening tool, not a definitive diagnosis. It should always be interpreted alongside the actual BUN and creatinine values, urine output, clinical history, and other labs like urinalysis and fractional excretion of sodium (FeNa).