How this calculator works
The conventional ratio divides BUN by creatinine after both are expressed in mg/dL. For SI urea, the conventional clinical conversion is BUN mg/dL = 2.8 × urea mmol/L. Do not enter whole-urea mass as BUN mass. Protein intake, bleeding, medicines, hydration and muscle mass can affect the result; the ratio alone cannot identify the cause of kidney dysfunction. The result is an estimate for information only and is not medical advice.
Formula
BUN/creatinine = BUN in mg/dL / creatinine in mg/dL. Creatinine mg/dL = creatinine micromol/L / 88.4. Urea mmol/L × 2.8 gives BUN mg/dL.
Worked example
BUN 20 mg/dL and creatinine 1 mg/dL give a ratio of 20. BUN 30 mg/dL and creatinine 2 mg/dL give 15.
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Frequently asked questions
Why not divide SI values directly?
Urea mmol/L and creatinine micromol/L describe different analytes and scales. Their raw ratio is not the conventional BUN/creatinine ratio.
Is BUN the same as urea?
BUN reports only the nitrogen mass within urea. Urea reports the whole molecule.
Does a high ratio prove dehydration?
No. Many kidney and non-kidney factors affect the numerator and denominator.