Bilirubin is a green-colored solution, which is released by the liver. This substance helps in the digestion process. The body synthesizes Bilirubin mainly through hemoglobin breakdown, which occurs when old red cells die.

Bilirubin levels rise in certain diseases. It is also responsible for the yellow color of injuries and the brown color fecal matter. Bilirubin level falls if the gut generates a product called urobilinogen, which is removed through the urine.

The unconjugated bilirubin refers to the water insoluble pigment before it reaches the liver. This pigment then gets converted into a water-soluble or conjugated bilirubin, which is then excreted into the bile. The blood test for total bilirubin is used to measure both unconjugated and conjugated bilirubin. This is useful in evaluating jaundice, anemia, and several liver diseases, such as hepatitis.

Bilirubin is an excretion product, and the body does not monitor its levels. Bilirubin levels indicate the balance between production and elimination. Therefore, there exists no average level of bilirubin.

Mild rises in bilirubin may occur due to Hemolysis or increased breakdown of RBCs and Gilbert's syndrome. However, very high levels of bilirubin may occur due to neonatal hyperbilirubinaemia. Hyperbilirubinaemia is a liver disorder where the newborn's liver is not able to correctly conjugate the bilirubin. It may also rise due to serious liver failure, cirrhosis, acute hepatitis, and Crigler-Najjar syndrome.