Direct bilirubin 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 Direct bilirubin:
- Optimal 0 – 0.3 mg/dL (0 – 5 μmol/L); out of range below 0 or above 0.3 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 | 0 – 0.3 | — | below 0 or above 0.3 |
| μmol/L | 0 – 5 | — | below 0 or above 5 |
No separate Sufficient band is currently defined for this marker.
What the evidence says
The band ends at the usual laboratory upper limit for direct (conjugated) bilirubin: less than 0.3 mg/dL, about 5 µmol/L (MedlinePlus; Roche method as used in NHS laboratories). The limit depends on the method: some laboratories report up to 0.4 mg/dL or 9 µmol/L, so read a borderline result against the laboratory's own range. This is a reference limit, not an optimal target; no narrower target has evidence behind it. A low or zero result is normal and is not flagged.
Sources
- Bilirubin blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal direct (conjugated) bilirubin is less than 0.3 mg/dL (less than 5.1 µmol/L); total bilirubin is 0.1 to 1.2 mg/dL. Matches Sera's upper edge of 0.3 mg/dL and 5 µmol/L. Reviewed 2/13/2025.
- Bilirubin (conjugated) — University Hospitals Sussex NHS Foundation Trust, Pathology, 2026 · Laboratory / reference-interval sourceAdult conjugated bilirubin 0 to 5 µmol/L, taken from the Roche Cobas Direct Bilirubin kit insert. Matches Sera's µmol/L row exactly. Last updated 19 May 2026.
- Bilirubin (Direct, Conjugated) — University Hospitals Birmingham NHS Foundation Trust, Pathology tests database, 2026 · Laboratory / reference-interval sourceTwo sites of one trust use different limits: below 5 µmol/L at Heartlands and below 9 µmol/L at Queen Elizabeth. Shows that 5 is in use and that the limit depends on the method.
- Bilirubin, Total/Direct, Serum (test 001214) sample report — Labcorp, 2016 · Laboratory / reference-interval sourceLabcorp's sample report prints a direct bilirubin interval of 0.00 to 0.40 mg/dL, slightly wider than Sera's 0.3. Report dated 2016; the interval may have been revised since.
What Bilirubin (Direct) measures
The part of bilirubin the liver has already processed and made water-soluble, ready to leave in bile. Also called conjugated bilirubin.
A raised direct bilirubin points at the liver's ability to move bile rather than at red blood cell turnover, so it separates a bile-flow problem from the harmless kind of raised bilirubin. It means little on its own and should be read against total bilirubin, ALP, and GGT. Analysers struggle to tell very small values apart, so small movements near zero are usually noise.