What Is a BUN/Creatinine Ratio Calculator?
A BUN/creatinine ratio calculator divides blood urea nitrogen (BUN) by serum creatinine to produce a ratio that helps clinicians evaluate kidney function and hydration status. Because BUN and creatinine are handled differently by the kidneys, their ratio can point toward whether a problem is prerenal (such as dehydration), intrinsic to the kidney, or postrenal (obstruction). Enter the two lab values and the calculator returns the ratio and its typical interpretation.
How to Use the Calculator
- Enter BUN — blood urea nitrogen in mg/dL.
- Enter serum creatinine — in mg/dL.
- Calculate — see the ratio and interpretation category.
The Formula
BUN/Creatinine Ratio = BUN ÷ Serum Creatinine
For example, a BUN of 40 mg/dL and creatinine of 1.0 mg/dL gives a ratio of 40, which is elevated and may suggest a prerenal cause.
Interpreting the Ratio
| Ratio | Typical Interpretation |
|---|---|
| 10:1 to 20:1 | Normal range |
| Greater than 20:1 | Prerenal cause (e.g., dehydration, GI bleed, low perfusion) |
| Less than 10:1 | Intrinsic renal cause or low protein/overhydration |
Why the Ratio Helps
- Hydration: a high ratio often reflects dehydration or reduced blood flow to the kidneys.
- Differentiating causes: it complements other tests in distinguishing prerenal from intrinsic kidney problems.
- Monitoring: trends over time can track response to fluids or treatment.
Important Caveats
The ratio is one piece of a larger clinical picture. Factors such as high-protein diet, gastrointestinal bleeding, certain medications, muscle mass, and liver disease can shift BUN or creatinine independently. Always interpret alongside symptoms, other labs, and clinical judgment.
Note: This calculator is an educational tool and does not replace professional medical evaluation.
Frequently Asked Questions
What is a normal BUN/creatinine ratio?
A normal ratio is generally between 10:1 and 20:1, though reference ranges vary slightly by laboratory.
What does a high BUN/creatinine ratio mean?
A ratio above 20:1 often suggests a prerenal cause such as dehydration, reduced blood flow, or gastrointestinal bleeding, where urea is reabsorbed more than creatinine.
What does a low ratio indicate?
A ratio below 10:1 may point to intrinsic kidney disease, a low-protein diet, overhydration, or liver disease affecting urea production.
How is the ratio calculated?
Divide the BUN value by the serum creatinine value, both in mg/dL. For instance, BUN 30 ÷ creatinine 1.0 = a ratio of 30.
Is this BUN/creatinine calculator free?
Yes — it is completely free, requires no signup, and returns the ratio with interpretation.