Conjugated bilirubin

Upper limits vary from about 3 to 8 depending on the method the lab uses; use the range printed.

Conjugated bilirubin, also called direct bilirubin, is the form of the pigment after the liver has processed it and made it water-soluble ready to pass into bile. When the bile ducts are blocked or the liver cells cannot pass it out, this form builds up in the blood and also appears in the urine. The test measures this fraction of the total bilirubin.

Doctors request it when the total bilirubin is raised, to work out whether the problem is before the liver (red cells breaking down, or Gilbert's syndrome) or in the liver and bile ducts. A high conjugated fraction points doctors towards the liver and bile ducts.

• Blockage of the bile ducts by gallstones, narrowing or a growth
• Hepatitis and other liver cell conditions
• Some medicines that slow bile flow
• Rare inherited conditions of bilirubin handling
• Bile flow problems in pregnancy

• It has no meaningful lower limit; a value near zero is the usual state in the general population

• Many labs only measure it when the total is raised, so it is often absent from reports
• Different methods give different upper limits
• It is unaffected by fasting, unlike total bilirubin, so a raised total with a low conjugated value is a common and often harmless pattern in the general population

No fasting needed. Read together with the total bilirubin from the same sample.

Written by a UK consultant physician. Typical UK adult reference ranges; your laboratory's own printed range takes precedence.