BUN optimal range and reference range
Compiled by Alina Radu, founder of Sera, from the published sources below · Last reviewed November 9, 2026
Sera's bands for BUN:
- Optimal 10 – 16 mg/dL; sufficient 6 – 20 mg/dL; out of range below 6 or above 20 mg/dL.
Evidence grade: Published reference interval. A band that primarily reflects a published adult laboratory or population reference interval. It is not necessarily applicable to every assay or laboratory.
All units
| Unit | Optimal | Sufficient | Out of range |
|---|---|---|---|
| mg/dL | 10 – 16 | 6 – 20 | below 6 or above 20 |
What the evidence says
The acceptable band is the general normal result given by MedlinePlus, 6 to 20 mg/dL. Laboratories differ: Mayo Clinic Laboratories reports 8 to 24 in men and 6 to 21 in women, so a result just above 20 may be printed as normal. BUN rises with dehydration, high protein intake and reduced kidney function and falls with low protein intake, so it is read with creatinine and eGFR. Outside the US the same test is reported as urea: urea in mmol/L is BUN in mg/dL multiplied by 0.357. The optimal band of 10 to 16 is a functional target with no published evidence behind it.
Sources
- BUN - blood test — MedlinePlus Medical Encyclopedia, U.S. National Library of Medicine, 2025 · Government / public-health guidanceNormal result is generally 6 to 20 mg/dL. Matches Sera's upper edge of 20; the lower edge is 6, not Sera's 7.
- BUN - Overview: Blood Urea Nitrogen (BUN), Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult reference values: men 8 to 24 mg/dL, women 6 to 21 mg/dL. Shows the interval is sex-specific at this laboratory and that upper limits above 20 are in use.
What BUN (Blood Urea Nitrogen) measures
The nitrogen part of urea, a waste product from protein breakdown that the kidneys filter out. This is the version reported by US labs.
High BUN can point to kidney trouble, dehydration, or eating a lot of protein, while low values can suggest liver disease or poor nutrition. BUN is not the same as Urea, where BUN (mg/dL) = Urea (mg/dL) ÷ 2.14. Read it alongside creatinine, eGFR, and uric acid as a kidney panel.