BUN/Creatinine Ratio Calculator

What is the BUN/creatinine ratio?

The BUN/creatinine ratio compares two kidney waste products - blood urea nitrogen (BUN) and creatinine - to give a clue about why a kidney number might be off. Both rise when the kidneys filter less, but urea also rises with dehydration, reduced blood flow and high protein turnover, while creatinine is steadier. So the ratio between them helps separate "the kidneys are short of fluid/blood flow" from "the kidney tissue itself is affected".

Urea or BUN? (Important for Indian reports)

Indian labs almost always report "blood urea", but the ratio is defined using BUN (blood urea nitrogen). They are not the same number: BUN = urea / 2.14, because urea contains two nitrogen atoms that make up about 47% of its weight. This calculator handles the conversion for you - just pick "Urea (mg/dL)" or "BUN (mg/dL)" on the toggle to match your report, and creatinine in mg/dL or micromoles per litre. Everything is calculated in your browser and nothing is stored.

What your result means

What abnormal values can mean

• High ratio - most often dehydration or reduced blood flow to the kidneys (a "prerenal" picture). It can also rise with gastrointestinal bleeding or a very high-protein diet.
• Low ratio - can reflect liver disease, low protein intake, or some intrinsic kidney conditions.

The ratio is only a pointer. It is read together with your creatinine, eGFR, urine tests and clinical picture, so take any abnormal value to your doctor rather than acting on it alone.