Blood and lab tests
What Does BUN/Creatinine Ratio Mean?
BUN/creatinine ratio · say it: B-U-N kree-AT-ih-neen RAY-shee-ohAlso written: BUN:Cr ratio, BUN/Cr, urea:creatinine ratio
Short answer
The BUN/creatinine ratio compares two kidney-related waste products to help doctors work out why one is out of range.
What it means
The BUN/creatinine ratio is not a separate measurement. The lab takes the BUN result and divides it by the creatinine result from the same blood sample. Both are waste products cleared by the kidneys, but they come from different sources: urea from protein breakdown and creatinine from muscle.
Labs print the ratio because BUN and creatinine do not always move together. If BUN rises much more than creatinine, the ratio goes up, which can happen with dehydration, reduced blood flow to the kidneys, bleeding in the upper gut or a high-protein diet. If both rise together, the kidneys themselves may be filtering less. A low ratio can be seen with liver disease, low protein intake or muscle breakdown. The ratio is a clue, not an answer.
The ratio is different from eGFR, which estimates how much blood the kidneys filter each minute. Some labs only print the ratio when BUN or creatinine is outside range.
Where you may see it
- Comprehensive metabolic panels from US labs
- Kidney function sections of hospital blood results
- Reports where the ratio line appears only when another value is flagged
📄 How it looks on a report
BUN/Creatinine Ratio 27 H
🙅 What it does not mean
- A high ratio does not mean the kidneys are failing. It often points to causes outside the kidneys, such as not drinking enough.
- The ratio does not replace the individual results. Doctors look at BUN, creatinine and eGFR first and use the ratio as extra context.
- A flagged ratio does not always mean either BUN or creatinine is flagged. When both numbers are small, a little change in one can move the ratio a lot.
🗒️ Questions to ask your doctor
🧾 Reports where you will see “BUN/creatinine ratio”
Paste or upload the report and every line of it is explained, with personal details removed first.
🔗 Read more from trusted sources
- “BUN/creatinine ratio” on MedlinePlus ↗
US National Library of Medicine
- MedlinePlus lab test guides ↗
US National Library of Medicine
Seeing this word on your own report? Get every line of it explained, free.
Explain my report🧩 Related words
🔎 Look up another word
More words: blood and lab tests
General information about a medical word, not advice about your own results. Ask the clinician who ordered the test what it means for you.