Indirect Bilirubin: What This Value Means

Bilirubin is formed when your body breaks down worn-out red blood cells. The pigment that is released enters your blood first as indirect (unconjugated) bilirubin, carried on the protein albumin. Your liver then converts it into direct (conjugated) bilirubin, which leaves your body in bile.

Indirect bilirubin is not measured separately in the laboratory. The value follows from a simple sum: indirect bilirubin is your total bilirubin minus your direct bilirubin, in the same unit. No extra blood sample is needed for it.

Splitting the total into two parts gives a sharper picture. The balance between the direct and the indirect fraction helps your doctor work out where an abnormal total is coming from.

A raised total bilirubin does not yet say where the problem lies. Splitting it into a direct and an indirect fraction does, because each fraction arises at a different stage of the same route.

When it is mainly the indirect fraction that is higher, the cause usually sits before the processing step in the liver: more bilirubin is being produced because red blood cells break down faster, or the liver processes it more slowly than usual. One well-known and generally harmless version of that is Gilbert's syndrome, in which this processing is naturally somewhat slower.

If the emphasis falls on the direct fraction instead, attention shifts to the drainage of bile or to the liver itself. Your doctor therefore never reads the indirect value on its own, but always alongside your total and direct bilirubin, the rest of your liver values and your symptoms.

Indirect bilirubin belongs to a bilirubin measurement that also looks at the total and the direct fraction. That is often done as part of a liver check, or when an earlier result gave reason to look further.

A measurement can also be useful with yellowing of the skin or the whites of the eyes, with a change in the colour of urine or stools, or with symptoms that may point to faster breakdown of red blood cells, such as persistent tiredness or paleness.

Bilirubin can vary from day to day and can be temporarily higher after a longer stretch without eating or during illness. A single result therefore says less than the picture across several measurements.