High bilirubin

Jaundice or icterus describes the yellow staining of the tissues due to an excess of bilirubin - unconjugated or conjugated.

Normal serum bilirubin is 3 to 17 micromol/l. Jaundice becomes clinically detectable at levels above 40 micromol/l. Good natural light is required to detect slight clinical jaundice.

Tissues which concentrate bilirubin best are those with a high content of elastic tissue, i.e. skin, ocular sclera, and blood vessels.

Raised bilirubin can be the result of raised excretion or raised production:

• raised production can be the result of obstructive liver disease - however other liver enzymes (alkaline phosphatase and gamma-GT) are usually increased
• in mechanical obstructive liver disease more than 50% of the bilirubin is conjugated bilirubin (1)

Isolated raised levels of bilirubin may be the result of a defect in conjugation of bilirubin e.g. in Gilbert's disease. In Gilbert's disease there is an increase in levels of unconjugated bilirubin. Other causes to consider if there is an isolated raised unconjugated bilirubin level include haemolysis. If haemolysis is suspected then this can be investigated via the reticulocyte count, blood film, haptoglobin measurement and lactate dehydrogenase levels (1).

Reference:

1. Doctor magazine (January 27th 2007), 45.