Approximately 80-85% of the bilirubin originates from the degradation of hemoglobin’s heme moiety, is subsequently transported into the liver where it is rapidly rendered soluble by glucuronidation, is excreted into biliary canaliculi, and is finally hydrolyzed in the gastrointestinal tract. Unconjugated bilirubin serum concentration increases in case of overproduction of bilirubin (acute or chronic haemolytic anemias) and in case of disorders of bilirubin metabolism or transport (impaired uptake by liver cells:Gilbert’s syndrome; defects in the conjugation reaction: Crigler-Najjar syndrome).Reduced excretion (hepatocellular damage such as hepatitis or cirrhosis; Dubin-Jonhson and Rotor syndromes) and obstruction to the flow of bile(most often produced by gallstones or by tumors) inducean important elevation of conjugated bilirubin and in a minor extent an increase of unconjugated bilirubin(conjugated hyperbilirubinemia).In clinical practice, serum bilirubin measurement in children and adults is indicated to help screen and follow-up of liver disorders and hemolytic anemia.