Urea is reabsorbed in the kidney when blood flow is low, while creatinine is not, so dehydration raises the ratio. The ratio is a clue rather than a diagnosis – high-protein diets, steroids and gut bleeding also raise it.
How to use the BUN to Creatinine Ratio Calculator
- BUN
- Creatinine
Results update as you type, and every field accepts the units shown in its menu.
How it works
Enter BUN (or urea) and creatinine from the same blood test.
Inputs explained
| Field | What to enter |
|---|---|
| BUN | Units: mg/dL, mmol/L urea |
| Creatinine | Units: mg/dL, µmol/L |
What each result means
- BUN/creatinine ratio = [BUN]÷[Creatinine]
- Urea/creatinine ratio (UK units, mmol/µmol) = ([BUN]÷2.8)÷([Creatinine]×88.42)×1000
Example values
How the main result changes when BUN changes and everything else stays at the example values above:
| BUN (mg/dL) | BUN/creatinine ratio |
|---|---|
| 10 | 10 |
| 15 | 15 |
| 20 | 20 |
| 25 | 25 |
| 30 | 30 |
| 40 | 40 |
Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.
Formula
BUN/Cr ratio = BUN (mg/dL) ÷ creatinine (mg/dL)
> 20: pre-renal or upper GI bleeding · 10–20: normal or post-renal · < 10: intrinsic kidney damage, liver disease or low protein intake
Worked example
Inputs — BUN: 20 mg/dL; Creatinine: 1 mg/dL.
Results — BUN/creatinine ratio = 20; Urea/creatinine ratio (UK units, mmol/µmol) = 81.
Key terms
- BUN
- Blood urea nitrogen.
Frequently asked questions
What is a normal BUN/creatinine ratio?
About 10–20.
What does a high ratio mean?
Often dehydration, heart failure, gut bleeding or a high-protein diet.
What does a low ratio mean?
Liver disease, malnutrition or intrinsic kidney damage.