Bilirubin, Indirect
The part of bilirubin that has not yet been processed by the liver. It is worked out by subtracting direct bilirubin from total bilirubin.
AI-drafted. Awaiting verificationAlso called I BILI, I BIL, IBILLOINC 1971-1
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What it is
Bilirubin is a yellow pigment made when old red blood cells break down. At first it is 'indirect', or unconjugated: it travels through the blood bound to albumin on its way to the liver. The liver then processes it so it can leave in bile. Labs usually don't measure indirect bilirubin directly. They subtract direct bilirubin from total bilirubin.
Why it matters
A raised indirect bilirubin means unprocessed bilirubin is building up. In adults the common reasons are red blood cells breaking down faster than usual and Gilbert syndrome, a harmless inherited trait that affects roughly 5% to 8% of people. Comparing indirect with direct bilirubin helps your clinician judge whether to look first at red cells or at the liver and bile ducts.
If it’s high
A level above your lab's range is often mild and has a harmless explanation, such as Gilbert syndrome, fasting or illness. Higher levels can be linked to faster red blood cell breakdown or to the liver being slower than usual at processing bilirubin.
Common causes
- Gilbert syndrome, a common and harmless inherited trait, with levels rising when fasting or sick
- Fasting or eating very little
- Red blood cells breaking down faster than usual (hemolysis)
- Reabsorption of a large bruise or collection of blood (hematoma)
- Some medicines
- Rare inherited conditions of bilirubin processing, such as Crigler-Najjar syndrome
What can help
- Ask whether a repeat test, a fasting sample, or a blood count would help explain the result
- Review your medicines and supplements with your clinician
- If Gilbert syndrome is the explanation, ask how fasting or illness might affect future results
Usual ranges
What labs print as the reference range, by who was tested. Ranges differ a little between labs, so the range on your own report is the one your result is judged against.
See Indirect bilirubin by age and sex, with the U.S. survey numbers where they exist.
What can affect your result
- Fasting or skipping meals, especially if you have Gilbert syndrome
- Illness and strenuous exercise
- Age: newborns normally run higher and have their own age-in-hours charts
- The total and direct bilirubin results it is calculated from
- Lab differences in how total and direct intervals are set
- Indirect bilirubin is calculated, so any problem with the total or direct result carries into it. When direct bilirubin is near zero, the calculated value is especially imprecise.
- Bilirubin breaks down in light, so labs protect the sample from light (ARUP, Mayo).
- Going without food can raise unconjugated bilirubin, especially in Gilbert syndrome. The British Society of Gastroenterology advises repeating an unexpected isolated rise on a fasting sample.
- Strenuous exercise and some medicines or foods can raise bilirubin (MedlinePlus). In Gilbert syndrome, illness can also raise it.
Changes with fasting or illness can appear within a day or two. After red cell breakdown or a liver problem is resolved, bilirubin can take weeks to settle fully.
When to talk to a clinician
Contact your clinician soon if your skin or eyes look yellow, your urine is dark, your stools are pale, or you have belly pain, itching or fever. A baby with yellow skin or eyes should be checked promptly by the baby's clinician, because safe levels depend on the baby's age in hours. Call 911 or your local emergency number for confusion, severe belly pain or fainting.
Questions you could ask
- If my bilirubin is mildly raised on its own, which other tests would help?
- Could Gilbert syndrome, fasting or illness explain this?
- Would a repeat test, a fasting sample or a blood count help?
- Could a medicine or supplement be involved?
Questions people ask
Why isn't indirect bilirubin measured directly?
Labs measure total bilirubin and direct bilirubin, and the report subtracts one from the other to give indirect bilirubin. This means a small error in either number shows up in the indirect value.
Does a high indirect bilirubin mean I have liver disease?
Not necessarily. Mild rises with otherwise usual liver tests are often due to Gilbert syndrome, fasting or faster red blood cell breakdown. Your clinician looks at your other liver tests and a blood count to sort out the cause.
Show the science and sources
Units
- 1 mg/dL = 1 mg/dL
- 1 mg/dL = 17.1 µmol/L
Open the Indirect bilirubin unit converter
For clinicians and researchers
Indirect bilirubin is calculated as total minus direct bilirubin, so it carries the error of both measurements and becomes unreliable when direct bilirubin is near zero. It is mostly unconjugated bilirubin bound to albumin, plus whatever the direct assay does not capture. In adults, unconjugated hyperbilirubinemia is usually hemolysis or Gilbert syndrome, which affects about 5% to 8% of people (BSG 2018; Giannini 2005); in Gilbert syndrome the indirect bilirubin usually does not exceed about 68 µmol/L (Giannini 2005). The BSG 2018 guideline advises repeating an isolated raised bilirubin with fractionation, a blood count and a fasting sample, and considering rarer causes such as Crigler-Najjar syndrome when unconjugated bilirubin exceeds 40 µmol/L. Reticulocyte count, LDH and haptoglobin help look for hemolysis. Reference intervals depend on how each lab sets its total and direct limits.
LOINC 1971-1 (primary), 14630-8, 35192-4. Specimen: calculated.
Sources
- Bilirubin, Total/Direct, Serum (test 001214), sample report, Labcorp
- Pediatric Testing Reference Ranges, Labcorp
- Bilirubin Blood Test, MedlinePlus, National Library of Medicine
- Guidelines on the management of abnormal liver blood tests, Gut (British Society of Gastroenterology) (2018)
- Liver enzyme alteration: a guide for clinicians, Canadian Medical Association Journal (2005)
- Bilirubin (PubChem CID 5280352), PubChem, National Library of Medicine
AI-drafted. Awaiting verification. Last reviewed 2026-10-03. How we build and check these pages.