Enter your Blood Urea Nitrogen (BUN) and Serum Creatinine values (both in mg/dL) to calculate your BUN to Creatinine Ratio. The tool instantly computes the ratio and interprets whether your result falls into the normal range (10–20), suggests possible pre-renal, intrinsic renal, or post-renal causes, and flags high or low values that may warrant further evaluation.
BUN to Creatinine Ratio
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Interpretation
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BUN
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Serum Creatinine
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A normal BUN to Creatinine ratio falls between 10 and 20. Values within this range generally reflect healthy kidney filtration, adequate hydration, and normal protein metabolism. Some clinical guidelines use a slightly narrower range of 10–15 for optimal health.
The ratio is calculated by simply dividing your Blood Urea Nitrogen (BUN) value by your Serum Creatinine value, both measured in mg/dL. For example, if your BUN is 26 mg/dL and your creatinine is 0.87 mg/dL, the ratio is 26 ÷ 0.87 ≈ 29.9.
A ratio above 20 may suggest pre-renal causes such as dehydration, reduced blood flow to the kidneys, high protein intake, gastrointestinal bleeding, or increased protein catabolism. It can also occur with certain medications like corticosteroids. This should be evaluated by a physician alongside other clinical findings.
A ratio below 10 may indicate low protein intake, severe liver disease (which reduces urea production), overhydration, or intrinsic kidney disease affecting tubular reabsorption. Rhabdomyolysis, which elevates creatinine disproportionately, can also produce a low ratio.
A ratio of 21 is mildly elevated above the normal range of 10–20. It may suggest slight dehydration, elevated protein intake, or early pre-renal stress. While it is not an alarming value on its own, it warrants attention to hydration status and should be interpreted alongside other lab values and clinical context.
Both BUN and creatinine are metabolic waste products filtered by the kidneys, but they behave differently. Creatinine is filtered and secreted into the tubular lumen and is not reabsorbed, making it a reliable filtration marker. BUN is filtered but partially reabsorbed back into the blood, so its levels are more sensitive to hydration status and protein metabolism, making the ratio clinically informative.
The BUN/Creatinine ratio is a useful screening and diagnostic aid, particularly for differentiating causes of acute renal failure (pre-renal, intrinsic renal, and post-renal), but it cannot diagnose kidney disease on its own. A physician will consider this ratio alongside GFR, urinalysis, imaging, and clinical symptoms to make a definitive diagnosis.
No. This calculator is intended for informational and educational purposes only. It does not replace the judgment of a qualified healthcare professional. Always consult your doctor or nephrologist to interpret your lab results in the context of your full medical history and clinical presentation.