Calculate the BUN/creatinine ratio from blood urea nitrogen (BUN) or urea and serum creatinine measured from the same blood draw. Unit choices are converted tothe conventional mg/dL ratio.
BUN/Creatinine Ratio Calculator
BUN/creatinine ratio
BUN/Cr = BUN (mg/dL) ÷ serum creatinine (mg/dL)
Conventional comparison range
BUN varies with protein intake, gastrointestinal bleeding, liver function and fluid status; creatinine varies with muscle mass and other factors. The ratio alone cannot diagnose dehydration, distinguish prerenal from intrinsic acute kidney injury, or assess kidney function. Acute kidney injury is evaluated using changes in creatinine and urine output, among other findings.
What the result means
10:1–20:1 is a commonly used comparison interval. A ratio above 20:1 may suggest factors such as reduced kidney perfusion, but it does not establish a cause. A low ratio is not a diagnosis either. Consider your laboratory interval, previous results and clinical context.
Limits
BUN varies with protein intake, gastrointestinal bleeding, liver function and fluid status; creatinine varies with muscle mass and other factors. The ratio alone cannot diagnose dehydration, distinguish prerenal from intrinsic acute kidney injury, or assess kidney function. Acute kidney injury is evaluated using changes in creatinine and urine output, among other findings.
What to check next
Check the original BUN and creatinine values from the same date, the creatinine trend, eGFR, urine output and symptoms. Seek prompt clinical advice for reduced urine output, suspected severe dehydration or a rapidly changing result.
Questions for a visit
- What are this lab’s BUN and creatinine intervals, and how have my values changed?
- How should eGFR, urine tests, medicines and fluid status be interpreted together?
- Which symptoms or changes need urgent assessment or repeat testing?
Inputs are calculated in this browser and are not automatically stored or sent to the site. Printing or saving a PDF includes the values.
How to use it and example
For BUN 20 mg/dL and serum creatinine 1.0 mg/dL, the ratio is 20:1. Urea 7.14 mmol/L and creatinine 88.4 µmol/L convert to about 20:1. The conversion is urea mmol/L × 2.80 = BUN mg/dL and creatinine µmol/L ÷ 88.4 = mg/dL.
What the result means
10:1–20:1 is a commonly used comparison interval. A ratio above 20:1 may suggest factors such as reduced kidney perfusion, but it does not establish a cause. A low ratio is not a diagnosis either. Consider your laboratory interval, previous results and clinical context.
Limits
BUN varies with protein intake, gastrointestinal bleeding, liver function and fluid status; creatinine varies with muscle mass and other factors. The ratio alone cannot diagnose dehydration, distinguish prerenal from intrinsic acute kidney injury, or assess kidney function. Acute kidney injury is evaluated using changes in creatinine and urine output, among other findings.
Frequently asked questions
Can I enter urea 20 mg/dL as BUN 20 mg/dL?
No. Urea mass and urea nitrogen mass differ. Multiply urea mg/dL by about 0.467 to obtain BUN mg/dL. Check the exact analyte printed on the lab report.
Does a ratio above 20:1 mean dehydration?
No. It is one clue affected by many factors. Studies found limited accuracy for distinguishing causes of acute kidney injury. A clinician considers creatinine changes, urine output, history and other tests.
Related calculators and records
eGFR calculator · CrCl calculator · Urine ACR calculator · Plasma osmolality calculator · Health records and visit preparation
Sources
- Labcorp, SI unit conversion table
- ED study of BUN/creatinine diagnostic performance (2017)
- KDIGO Acute Kidney Injury guideline (2012)
General health information, not a substitute for diagnosis or care. No independent clinician review is claimed. · Sources checked 2026-09-30