Explainer · updated 2026-11-09
Bilirubin, explained in plain English
Key facts
- Typical adult reference interval: 0.3-1.0 mg/dL (ABIM)
- The same interval in umol/L: 5.1-17.1 umol/L (ABIM)
- What bilirubin is: the yellow pigment left when old red cells are broken down, cleared by the liver into bile (ACG 2017)
- What enough of it in the blood turns yellow: the skin and the whites of the eyes, which is what jaundice is (ACG 2017)
- What a high level can come from: a blocked bile flow or damaged liver cells (ACG 2017)
What it is
Bilirubin is the yellow pigment left when old red cells are broken down. The liver clears it into bile. Enough of it in the blood turns the skin and the whites of the eyes yellow, and that is what jaundice is.
What the number is telling you
The report usually gives a total and a direct fraction. The direct fraction is the part the liver has already processed, and the split between the two is what points your doctor towards the cause. A mild rise with normal liver enzymes is common.
What high or low can mean
High: A high level can come from a blocked bile flow or from damaged liver cells, so the direct fraction is measured next.
Low: A low figure has been linked to a higher risk of heart disease, and it is not treated as a good sign.
What a typical result looks like
Typical adult reference intervals from ABIM run from 0.3 to 1.0 mg/dL, about 5.1 to 17.1 umol/L. The range on your own report is the one that counts.
Questions worth asking your doctor
- What is my direct fraction, and what does the split suggest?
- Were my liver enzymes normal beside it?
- How does this compare with my previous results?
If a result worries you, ask your doctor.
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