Bilirubin is a yellow-orange pigment, produced by the process of excretion when red blood cells are broken down physiologically in the blood, then passes through the liver and finally out of the body. Therefore, quantitative Bilirubin testing will help support the determination of some abnormalities in the liver-bile and hemolysis.

Bilirubin is the end product of hemoglobin metabolism and is derived primarily from the breakdown of red blood cells, to a lesser extent from cytochromes and myoglobin.