Several diseases are associated with hyperbilirubinemia. Direct and indirect bilirubin values are used in the differential diagnosis of hyperbilirubinemia.
Hyperbilirubinemia could be caused by
increased bilirubin production
decreased uptake into the liver cells
impaired conjugation
interference with the secretion of conjugated bilirubin.
Here is a schematic diagram that represents normal bilirubin metabolism. Use this to compare with various abnormal states described below. Clicking on the diagrams will reveal larger versions of them.
Here are some examples of diseases in which hyperbilirubinemia is observed.
Hemolytic jaundice
results in increased production of bilirubin.
Here more bilirubin is conjugated and excreted than normally, but the conjugation mechanism is overwhelmed, and an abnormally large amount of unconjugated bilirubin is found in the blood.
Gilbert's disease
may be caused by an inability of the hepatocytes to take up bilirubin from the blood.
As a result, unconjugated bilirubin accumulates.
Physiological jaundice and Crigler-Najjar syndrome
are conditions in which conjugation is impaired.
Unconjugated bilirubin is retained by the body.
Dubin-Johnson syndrome
is associated with inability of the hepatocytes to secrete conjugated bilirubin after it has been formed.
Conjugated bilirubin returns to the blood.
Biliary obstruction
by (for example) biliary calculi causes backup and reabsorption of conjugated bilirubin.
