Bilirubin is formed as a result of hemoglobin degradation. Normally, senescent red blood cells are removed from circulation and the bilirubin that is formed is processed by the liver. The normal level of bilirubin in the serum of adults is 0.2-1mg/dl.

Bilirubin levels increase with liver disorders and also in anemia that is a result of a hemolytic process. Patients may display jaundice when serum bilirubin levels exceed 2mg/dl.

Persons with alpha thalassemia intermedia usually have an increased bilirubin level, because of ongoing hemolysis. This bilirubin is typically the unconjugated fraction of bilirubin.