BUN to Creatinine Ratio
Compares blood urea nitrogen and creatinine to suggest causes of kidney injury.
When to use
Adults with acute kidney injury or kidney function assessment, to raise hypotheses about the cause.
Pearls and pitfalls
- The ratio uses blood urea nitrogen and creatinine, both in mg/dL.
- Values above 20 can occur in hypovolemia, gastrointestinal bleeding and catabolism.
- The ratio does not confirm the cause and does not replace volume and urine sediment assessment.
- Liver disease and low protein diet can reduce urea and the ratio.
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Formula
Ratio = blood urea nitrogen (mg/dL) / serum creatinine (mg/dL).
Evidence
Ratio used in the initial assessment of acute kidney injury, with limitations described in clinical cohorts.
References
- Uchino S, Bellomo R, Goldsmith D. The meaning of the blood urea nitrogen/creatinine ratio in acute kidney injury. Clin Kidney J. 2012;5(2):187-191. doi:10.1093/ckj/sfs013
Frequently asked questions
What is BUN to Creatinine Ratio?
Compares blood urea nitrogen and creatinine to suggest causes of kidney injury. Adults with acute kidney injury or kidney function assessment, to raise hypotheses about the cause.
How is the result calculated?
Ratio = blood urea nitrogen (mg/dL) / serum creatinine (mg/dL).
How should the result be interpreted?
Ratio used in the initial assessment of acute kidney injury, with limitations described in clinical cohorts.
What are the sources?
Uchino S, Bellomo R, Goldsmith D. The meaning of the blood urea nitrogen/creatinine ratio in acute kidney injury. Clin Kidney J. 2012;5(2):187-191.