Total 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 Total bilirubin:
- Optimal 0.3 – 1 mg/dL (5 – 17 μmol/L); sufficient 0.2 – 1.2 mg/dL (3 – 21 μmol/L); out of range above 1.2 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 | 0.3 – 1 | 0.2 – 1.2 | above 1.2 |
| μmol/L | 5 – 17 | 3 – 21 | above 21 |
Bounded on the high side only — a low result is not treated as out of range. Most laboratory intervals have no lower limit (mayo 0.0, york nhs none) and no source gives a low bilirubin a clinical meaning.
What the evidence says
The acceptable band ends at the adult upper reference limit used by Mayo Clinic Laboratories, MedlinePlus and NHS laboratories: 1.2 mg/dL, or 21 µmol/L. A low result is not flagged, because most laboratories set no lower limit and no source gives a low bilirubin a clinical meaning. The optimal band of 0.3 to 1.0 mg/dL is a functional target with no published threshold behind its upper edge. An isolated raised unconjugated bilirubin with a normal blood count and normal liver enzymes commonly reflects Gilbert's syndrome, a benign inherited variant; the British Society of Gastroenterology guideline says such people should be fully reassured.
Sources
- BILI3 - Overview: Bilirubin, Serum — Mayo Clinic Laboratories, 2026 · Laboratory / reference-interval sourceAdult total bilirubin 0.0 to 1.2 mg/dL. Matches Sera's sufficient upper edge of 1.2; the interval has no lower limit above zero.
- Bilirubin blood test — MedlinePlus Medical Encyclopedia, US National Library of Medicine, 2025 · Government / public-health guidanceNormal total bilirubin 0.1 to 1.2 mg/dL (1.71 to 20.5 µmol/L). Matches Sera's upper edge in both units; its floor is 0.1, not 0.2.
- Liver Function Test Reference Ranges in Normal Pregnancy — Scarborough, Hull and York Pathology Service, York and Scarborough Teaching Hospitals NHS Foundation Trust, 2022 · Laboratory / reference-interval sourceNon-pregnant adult total bilirubin below 21 µmol/L, with no lower limit. Matches Sera's upper edge of 21 µmol/L.
- Assessing liver function and interpreting liver blood tests — NHS Specialist Pharmacy Service, 2024 · Government / public-health guidanceNormal bilirubin 5 to 21 µmol/L. Matches the upper edge of 21 and is the only source found that quotes a lower limit (5 µmol/L, Sera's optimal floor).
- Guidelines on the management of abnormal liver blood tests — Newsome PN, Cramb R, Davison SM, et al. — Gut (British Society of Gastroenterology), 2018 · Clinical guidelineAn isolated raised bilirubin is most often Gilbert's syndrome, which is not associated with liver disease or ill health. Supports the note, not a band edge.
What Bilirubin (Total) measures
A yellow pigment made when old red blood cells break down. The liver processes it and removes it in bile, so it reflects both liver function and red blood cell turnover.
Mildly raised bilirubin is often harmless and a common cause is Gilbert's syndrome, which affects about 5-10% of people. Persistently high levels can point to liver disease, a blocked bile duct, or red blood cells breaking down too fast. Mildly raised bilirubin is actually linked to some heart protection because it acts as an antioxidant. Best read alongside ALT, AST, GGT, and ALP.