Urea 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 Urea:
- Optimal 3.5 – 6 mmol/L (21 – 36 mg/dL); sufficient 2.5 – 7.8 mmol/L (15 – 47 mg/dL); out of range below 2.5 or above 7.8 mmol/L.
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 |
|---|---|---|---|
| mmol/L | 3.5 – 6 | 2.5 – 7.8 | below 2.5 or above 7.8 |
| mg/dL | 21 – 36 | 15 – 47 | below 15 or above 47 |
What the evidence says
The acceptable band is the UK harmonised laboratory interval for adults, 2.5 to 7.8 mmol/L (15 to 47 mg/dL of urea). US laboratories report urea nitrogen (BUN) instead: urea in mg/dL is 2.14 times BUN in mg/dL, so the two must not be read against each other's ranges. Urea rises with dehydration, high protein intake and reduced kidney function and falls with low protein intake, so it is read with creatinine and eGFR. The optimal band is a functional target with no published evidence behind it.
Sources
- Urea (Pathology tests database) — University Hospitals Birmingham NHS Foundation Trust, 2026 · Laboratory / reference-interval sourceUK harmonised adult interval (Pathology Harmony) 2.5 to 7.8 mmol/L. Exactly Sera's acceptable band.
- Urea — North Bristol NHS Trust, Severn Pathology, 2026 · Laboratory / reference-interval sourceReference range 2.5 to 7.8 mmol/L, the same harmonised interval.
What Urea measures
A waste product made when the body breaks down protein, then filtered out by the kidneys. This test measures the whole urea molecule and is the version reported by UK, EU, and Australian labs.
High urea can point to kidney trouble, dehydration, or eating a lot of protein, while low values can suggest liver disease or poor nutrition. Urea is not the same as BUN, where Urea (mg/dL) = BUN (mg/dL) × 2.14. Read it alongside creatinine, eGFR, and uric acid as a kidney panel.