Avoid strong sunlight on sample. High direct in Gilberts syndrome. High indirect in haemolysis
Direct bilirubin (sometimes referred to as conjugated) is the form of bilirubin which has been conjugated with glucoronic acid and is excreted in the bile. Measurement of this metabolite is of assistance in diagnosis and monitoring of the many disease states associated with raised bilirubin.
Direct bilirubin also generates a value for the indirect (unconjugated) bilirubin when the total bilirubin level is known.
The disease states associated with increased bilirubin are generally divided into three types, pre-hepatic, hepatic and post hepatic. Pre-hepatic jaundice is typically caused by haemolytic anaemias, which have a large component of indirect bilirubin. Post-hepatic jaundice is usually caused by tumours of the head of the pancreas blocking the bile duct and gall stones, in such cases the bilirubin is mostly direct.
Hepatic jaundice may be variable: liver tumours produce mainly direct bilirubin, whilst conjugation defects, such as gilberts syndrome, have elevated indirect bilirubin.
In haemolytic disease of the newborn, the indirect bilirubin may become so high that it passes across the blood-brain barrier and is taken up by the fatty elements in the brain, producing kernicterus. Exchange transfusions are necessary to minimise this transfer.
Adult: 0 – 8 µmol/l
Serum or Lithium Heparin Plasma