BUN Creatinine Ratio Calculator – Kidney Function Check
Compute the BUN/creatinine ratio with mg/dL and SI unit support, plus interpretation guidance.
How to Use
- Enter the measured BUN value and choose the laboratory unit.
- Enter the creatinine value in the reported unit.
- Click Calculate to see the normalized mg/dL values, the BUN/creatinine ratio, and an interpretation badge.
- Review the clinical interpretation and correlate with patient presentation and other labs.
Understanding the BUN/creatinine ratio
The ratio compares nitrogenous waste (BUN) to creatinine, a byproduct of muscle metabolism. Because both markers are filtered by the kidneys, the ratio highlights disproportionate changes that may signal prerenal, renal, or postrenal pathology.
- Low ratios can indicate intrinsic renal damage or reduced urea synthesis in liver disease.
- Normal ratios suggest the BUN and creatinine are rising or falling together, as seen in many stable patients.
- High ratios often reflect prerenal causes such as dehydration, heart failure, or gastrointestinal bleeding.
Clinical considerations
Always interpret the ratio alongside absolute BUN and creatinine values, urine studies, medications, and symptoms. Volume depletion, high-protein diets, corticosteroids, and GI bleeding can elevate BUN disproportionately, while advanced liver disease or malnutrition can suppress it.
Trend the ratio over time. A sudden shift from normal to high may signal acute prerenal azotemia, whereas chronically low ratios can point toward long-standing hepatic impairment.
Frequently Asked Questions
- What is a critical BUN/creatinine ratio?
- Ratios above 30:1 deserve urgent evaluation for dehydration, gastrointestinal bleeding, or catabolic stress, especially when accompanied by elevated absolute BUN.
- Should I correct the ratio for age?
- There is no age correction for the ratio itself, but elderly patients may have lower baseline creatinine because of reduced muscle mass. Always review the absolute creatinine trend.
- Can medications skew the ratio?
- Yes. High-dose steroids, tetracyclines, or GI bleeding can raise BUN, while creatinine may shift with ACE inhibitors, ARBs, or nephrotoxic drugs. Consider the full medication list.