BUN to Creatinine Ratio

A ratio within the normal range indicates balanced kidney function and appropriate hydration status. The normal adult reference range for the BUN to creatinine ratio is 10:1 to 20:1, although laboratories may vary. The expected BUN-to-creatinine ratio for a healthy individual consuming about 70 grams of protein daily is 10:1 to 20:1. The ratio has a non-linear relationship to kidney function. Clinically detectable changes in the ratio typically appear only after about 50% or more renal function loss. Lifestyle factors can shift the ratio without indicating pathology. The BUN to creatinine ratio is calculated by dividing BUN in mg/dL by creatinine in mg/dL. After the 50% threshold is crossed, small additional kidney function reductions can produce large ratio changes. The test is described as a simple blood draw performed as part of a comprehensive metabolic panel, with 8 to 12 hours of fasting considered ideal. A normal ratio can occur despite 40% functional loss, creating false-negative risk if used alone. Deviations from the normal ratio can suggest kidney dysfunction, dehydration, or heart failure.