The blood urea nitrogen (BUN) to creatinine ratio is a calculation derived from two laboratory measurements: blood urea nitrogen (BUN) and serum creatinine. It is determined by dividing the BUN value (expressed in mg/dL) by the creatinine value (also expressed in mg/dL). For instance, if a patient’s BUN level is 20 mg/dL and their creatinine level is 1 mg/dL, the calculated ratio would be 20:1.
This ratio provides clinicians with valuable information regarding kidney function and hydration status. Elevated ratios may suggest conditions such as dehydration, upper gastrointestinal bleeding, or increased protein catabolism. Lower ratios may indicate liver disease or malnutrition. Historically, the ratio has been utilized as a readily available indicator to aid in the differential diagnosis of various renal and extra-renal conditions affecting kidney function.