What is my BUN creatinine ratio?
Enter blood urea nitrogen (BUN) and creatinine from the same blood test, in mg/dL or SI units, to get the BUN to creatinine ratio. For information only. This is not medical advice or a diagnosis. Do not use it to make treatment decisions without a clinician. No licensed clinician has reviewed this page.
- BUN:creatinine ratio
- 18
The BUN to creatinine ratio is 18: Usual range (10 to 20).
Usual range (10 to 20)
- Low (under 10)
- Usual range (10 to 20)
- High (over 20)
- Range
- Usual range (10 to 20)
- Urea:creatinine ratio (SI)
- 73
BUN:creatinine ratio: 18. The BUN to creatinine ratio is 18: Usual range (10 to 20).
Where does the ratio sit?
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Divides blood urea nitrogen (BUN) by serum creatinine, or urea by creatinine in SI units, and shows whether the ratio is in the usual 10 to 20 range.
Example with the default inputs (Units US (mg/dL), BUN (mg/dL) 18, Creatinine (mg/dL) 1): The BUN to creatinine ratio is 18: Usual range (10 to 20).
Method: Ratio = BUN (mg/dL) ÷ creatinine (mg/dL). SI: BUN = urea (mmol/L) × 2.8014; creatinine (mg/dL) = µmol/L ÷ 88.4; SI ratio = urea (mmol/L) ÷ creatinine (mmol/L).
- BUN and creatinine from the same blood sample.
- The ratio is rounded to 1 decimal and read from the rounded value: under 10 low, 10 to 20 usual, over 20 high.
- The ratio alone does not show the cause; it is read with the separate BUN and creatinine values.
Worked examples
Each example is checked against the calculator on every build.
- Units US (mg/dL), BUN (mg/dL) 18, Creatinine (mg/dL) 1 gives BUN:creatinine ratio 18, Range Usual range (10 to 20), Urea:creatinine ratio (SI) 73.
- Units US (mg/dL), BUN (mg/dL) 40, Creatinine (mg/dL) 1.2 gives BUN:creatinine ratio 33.3, Range High (over 20).Source: 40 ÷ 1.2 = 33.33, over 20 (Hosten 1990)
- Units SI (mmol/L, µmol/L), Urea (mmol/L) 5, Creatinine (µmol/L) 176.8 gives BUN:creatinine ratio 7, Range Low (under 10), Urea:creatinine ratio (SI) 28.
- Units US (mg/dL), BUN (mg/dL) 20, Creatinine (mg/dL) 1 gives BUN:creatinine ratio 20, Range Usual range (10 to 20).
Medical disclaimer
This calculator is for information and education only. It is not medical advice, and its result is not a diagnosis. Do not use it to start, stop, or change a treatment without a clinician who knows your health history. No licensed clinician has reviewed this page. This site's editors checked the formulas and worked examples against published sources. If you think you have a medical emergency, call your local emergency number.
When this does not apply. The ratio needs BUN (or urea) and creatinine from the same blood sample. The usual range of about 10 to 20 is a general guide: each lab sets its own range, and the ratio alone does not show the cause of abnormal kidney tests.
How the ratio is worked out
BUN:creatinine ratio = BUN (mg/dL) ÷ creatinine (mg/dL)
With SI units:
- BUN (mg/dL) = urea (mmol/L) × 2.8014. One mmol of urea holds 2 mmol of nitrogen, 2 × 14.007 = 28.014 mg, and 28.014 mg/L is 2.8014 mg/dL.
- Creatinine (mg/dL) = creatinine (µmol/L) ÷ 88.4 (KDIGO 2012).
The page also shows the SI form, urea (mmol/L) ÷ creatinine (mmol/L), where creatinine in mmol/L is µmol/L ÷ 1,000. It equals the US ratio × 88.4 ÷ 2.8014 (about 31.6 times the US ratio) and is rounded to a whole number.
Ranges
The US ratio is rounded to 1 decimal place (halves round up, read from the decimal value: a result within 1e-9 (relative) of a half counts as the half, so 2.005 rounds to 2.01) and read from the rounded value:
| Ratio | Reading |
|---|---|
| under 10 | low |
| 10 to 20 | usual range |
| over 20 | high |
Inputs the calculator accepts
BUN 1 to 300 mg/dL (urea 0.36 to 107 mmol/L), creatinine 0.1 to 20 mg/dL (8.84 to 1,768 µmol/L).
Worked examples by hand
The default. BUN 18, creatinine 1.0: 18 ÷ 1.0 = 18.0, usual range. SI: urea = 18 ÷ 2.8014 = 6.4254 mmol/L, creatinine = 88.4 µmol/L = 0.0884 mmol/L, 6.4254 ÷ 0.0884 = 72.7, shown as 73.
High. BUN 40, creatinine 1.2: 40 ÷ 1.2 = 33.3, over 20.
SI units, low. Urea 5 mmol/L and creatinine 176.8 µmol/L: BUN = 5 × 2.8014 = 14.007 mg/dL, creatinine = 176.8 ÷ 88.4 = 2.0 mg/dL, ratio = 14.007 ÷ 2.0 = 7.0, under 10. SI ratio = 5 ÷ 0.1768 = 28.3, shown as 28.
Top of the range. BUN 20, creatinine 1.0: 20.0, still the usual range.
Other questions people ask
What is the BUN creatinine ratio?
It is the blood urea nitrogen (BUN) divided by the serum creatinine, both in mg/dL. Both are waste products that the kidneys clear, but the body handles them differently, so their ratio can hint at why kidney tests are abnormal.
What is a normal BUN creatinine ratio?
The ratio is usually about 10 to 20. Labs set their own reference range, so check the one on your report.
What does a high BUN creatinine ratio mean?
A ratio over 20 is often seen when less blood reaches the kidneys (for example dehydration or heart failure), with bleeding in the stomach or upper gut, with a high protein intake, or with steroid treatment. It is a clue, not a diagnosis.
What does a low BUN creatinine ratio mean?
A ratio under 10 can go with a low protein intake, severe liver disease (the liver makes urea), or muscle breakdown that raises creatinine. It can also be normal in some people.
How do I convert urea in mmol/L to BUN?
Multiply urea in mmol/L by 2.8014 to get BUN in mg/dL, because each urea molecule holds two nitrogen atoms (2 × 14.007 g/mol). Divide creatinine in µmol/L by 88.4 to get mg/dL. The page does this for you.