Free tool

BUN to Creatinine Ratio Calculator

Q: What is a normal BUN to creatinine ratio?

About 10:1 to 20:1 when both are in mg/dL. Laboratories do not always print the ratio, and it is not a test result in itself — it is a comparison of two results that move for different reasons, so the absolute BUN, creatinine and eGFR are read first and the ratio second.

Q: What causes a high BUN to creatinine ratio?

Anything that raises urea faster than creatinine: dehydration or reduced blood flow to the kidneys (the classic 'prerenal' pattern), a high-protein diet or protein supplements, blood in the gut being digested, corticosteroids, heart failure, and urinary obstruction. Rehydration and a repeat panel sort out most outpatient cases.

Q: Can the ratio tell dehydration from kidney disease?

Only roughly. A high ratio with a normal creatinine favors dehydration or diet; both values high with a normal ratio favors the kidney itself. In hospital patients the ratio is notoriously unreliable because steroids, feeding, bleeding and liver disease change BUN on their own — which is why the eGFR and the clinical picture carry the decision.

The short answer

Enter BUN and creatinine from the same metabolic panel and the calculator divides them. A ratio of about 10–20 is usual; above 20 means urea is rising faster than creatinine, as in dehydration, reduced kidney blood flow, a high-protein intake, gut bleeding or steroids; below 10 points to liver disease, low protein intake or a high creatinine from muscle. A clue to read with the eGFR, not a diagnosis.

Inputs: BUN · creatinine
Usual ratio: ≈ 10–20
Read with: eGFR · hydration · diet
Cost: Free

BUN (urea nitrogen)

mg/dL

BUN range

Creatinine

mg/dL

Creatinine range

Enter your values to calculate.

BUN:creatinine = BUN [mg/dL] ÷ creatinine [mg/dL] (both in US units; the SI urea:creatinine ratio uses different cut points)

Educational — a derived index, not a diagnosis. Nothing you enter leaves your browser.

How the BUN:creatinine ratio is calculated

BUN:creatinine = BUN [mg/dL] ÷ creatinine [mg/dL] (both in US units; the SI urea:creatinine ratio uses different cut points)

Worked example

BUN (urea nitrogen) (mg/dL)	Creatinine (mg/dL)	BUN:creatinine ratio
18	1	18.0

Urea:creatinine (SI units): 73 (mmol/L ÷ µmol/L × 1000)

Falls in: Within the usual range.

How to read the result

BUN:creatinine ratio	Reads as	What it usually means
< 10	Low	A ratio under 10 usually means BUN is low relative to creatinine: a low-protein diet, liver disease (the liver makes urea), overhydration or pregnancy — or a creatinine that is high for the BUN, as in muscular people or after muscle injury. It is rarely a kidney problem in itself.
10 – 20	Within the usual range	About 10–20 is the expected ratio when the kidney is handling both substances normally and intake is ordinary. When both BUN and creatinine are high with a normal ratio, the pattern suggests the kidney itself (intrinsic kidney disease) rather than reduced blood flow to it.
20 – 30	Elevated	A ratio above 20 points to BUN rising faster than creatinine: dehydration or reduced kidney blood flow (prerenal), a high-protein diet or protein supplements, bleeding into the gut (digested blood is a protein load), corticosteroids, or heart failure. Hydration and a repeat panel are usually the first step.
≥ 30	Markedly elevated	Ratios of 30 and above are strongly disproportionate — significant volume depletion, upper gastrointestinal bleeding or urinary obstruction are the classic causes. With an elevated creatinine or symptoms (dizziness, black stools, very low urine output) this needs prompt medical evaluation.

Cut points reviewed by Youmna DiStefano, MD on 2026-10-12. Sources below.

Limits

The ratio is a rough bedside clue, not a diagnosis, and it misleads in the critically ill: steroids, high-protein feeding, GI bleeding and liver disease change BUN independently of kidney function, while muscle mass, age, sex and some drugs change creatinine. It should be read with the eGFR, the absolute values and the clinical picture; a persistently abnormal ratio with a normal eGFR in someone who feels well is usually diet or hydration.

Sources

Uchino S, Bellomo R, Goldsmith D. The meaning of the blood urea nitrogen/creatinine ratio in acute kidney injury. Clin Kidney J 2012;5:187–191. doi.org/10.1093/ckj/sfs013
Manoeuvrier G, et al. Diagnostic performance of serum blood urea nitrogen to creatinine ratio for distinguishing prerenal from intrinsic acute kidney injury in the emergency department. BMC Nephrol 2017;18:173. doi.org/10.1186/s12882-017-0591-9
Rachoin JS, et al. The fallacy of the BUN:creatinine ratio in critically ill patients. Nephrol Dial Transplant 2012;27:2248–2254. doi.org/10.1093/ndt/gfr705

Frequently asked questions

What is a normal BUN to creatinine ratio?

About 10:1 to 20:1 when both are in mg/dL. Laboratories do not always print the ratio, and it is not a test result in itself — it is a comparison of two results that move for different reasons, so the absolute BUN, creatinine and eGFR are read first and the ratio second.

What causes a high BUN to creatinine ratio?

Anything that raises urea faster than creatinine: dehydration or reduced blood flow to the kidneys (the classic 'prerenal' pattern), a high-protein diet or protein supplements, blood in the gut being digested, corticosteroids, heart failure, and urinary obstruction. Rehydration and a repeat panel sort out most outpatient cases.

Can the ratio tell dehydration from kidney disease?

Only roughly. A high ratio with a normal creatinine favors dehydration or diet; both values high with a normal ratio favors the kidney itself. In hospital patients the ratio is notoriously unreliable because steroids, feeding, bleeding and liver disease change BUN on their own — which is why the eGFR and the clinical picture carry the decision.

Which biomarkers does this tool cover?

Which tests give you these numbers?

Physician-authorized, drawn at Quest, Labcorp or BioReference. Results in 1–3 business days for most tests.