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.
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
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.
- Blood levels of conjugated bilirubin increase.