Bilirubin is a degradation product of Heme - a component of Hemoglobin in red blood cells. The degradation process occurs in the reticuloendothelial cells such as the liver, spleen, and bone marrow.

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.