Indirect (Unconjugated) Bilirubin Calculator
Indirect (Unconjugated) Bilirubin Calculator
Calculate indirect bilirubin from total and direct, and see the conjugated fraction that determines the differential.
Indirect (Unconjugated) Bilirubin
Total − directTotal 1.4 mg/dL, direct 0.6 mg/dL
Formula
Conjugated fraction (%) = direct ÷ total × 100
- indirect
- unconjugated bilirubin, albumin-bound and not water-soluble
- µmol/L
- multiply the mg/dL result by 17.1
Worked example
Total 1.4 mg/dL, direct 0.6 mg/dL
1.4 − 0.6 = 0.80 mg/dL indirect (13.7 µmol/L)
Conjugated fraction = 0.6 ÷ 1.4 = 43%
Causes of unconjugated hyperbilirubinaemia
| Mechanism | Examples |
|---|---|
| Increased production | Haemolysis, ineffective erythropoiesis, large haematoma, transfusion |
| Reduced uptake | Heart failure, portosystemic shunt, rifampicin |
| Reduced conjugation | Gilbert syndrome, Crigler-Najjar, neonatal physiological jaundice, hyperthyroidism |
Reading the split
Laboratories measure total and direct bilirubin; indirect is calculated as the difference. Because it is a subtraction of two measured values, a small direct result carries proportionally large analytical error, and an indirect fraction derived from a near-normal total should not be over-interpreted.
The split matters because it separates two entirely different differentials. An unconjugated rise means bilirubin is being produced faster than it can be conjugated, or that conjugation itself is impaired. The commonest cause by a wide margin is Gilbert syndrome — a reduced-activity UGT1A1 variant present in several per cent of the population, which produces an isolated unconjugated bilirubin that rises with fasting, illness or exertion and is entirely benign.
The important alternative is haemolysis, and it is straightforward to exclude: a reticulocyte count, LDH and haptoglobin alongside the film will settle it. If those are normal and the rest of the liver panel is normal, an isolated unconjugated hyperbilirubinaemia in the 1 to 3 mg/dL range needs no imaging, no hepatology referral and no repeat monitoring.
Frequently asked questions
How do I calculate indirect bilirubin?
Subtract direct from total. Laboratories measure the first two and report indirect as the difference, so it inherits the error of both.
What is a normal indirect bilirubin?
Up to about 1.0 mg/dL, or 17 µmol/L. Gilbert syndrome typically gives 1.2 to 3 mg/dL total with a normal direct fraction.
Does a raised indirect bilirubin need investigation?
Check a reticulocyte count, LDH and haptoglobin to exclude haemolysis. If those and the rest of the liver panel are normal, an isolated mild elevation is almost always Gilbert syndrome and needs nothing further.
Can Gilbert syndrome cause symptoms?
It causes mild jaundice during fasting, illness or exertion but no liver damage. It does affect the metabolism of a few drugs, notably irinotecan, which is worth knowing before chemotherapy.
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References
- Fevery J. Bilirubin in clinical practice: a review. Liver Int. 2008;28(5):592–605.
- Kwo PY, Cohen SM, Lim JK. ACG Clinical Guideline: evaluation of abnormal liver chemistries. Am J Gastroenterol. 2017;112(1):18–35.