Bilirubin is the orange-yellow pigment responsible for the skin colour of patients with jaundice and is formed as a product of the catabolism of haemoglobin. Total Bilirubin is made up of two forms Direct (conjugated) and Indirect (unconjugated).
Indirect Bilirubin is transported through the blood (bound to albumin) to the liver where it is conjugated with glucoronic acid to form the direct bilirubin. This direct bilirubin, in its water soluble conjugated glucoronide, form enters the biliary system for excretion in the bile.
Elevated bilirubin levels can be seen in a variety of conditions including haemolytic disorders, biliary obstruction, cholestasis, hepatitis, cirrhosis and decreased conjugation (e.g. neonatal jaundice).
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.
1 – 21 µmol/L
Serum or Lithium Heparin Plasma