Bilirubin, a heme catabolism end-product is produced by the reduction of its metabolic precursor biliverdin by the action of enzyme biliverdin reductase.

Bilirubin has been used as an interfering substance for in vitro interference and stability tests for myoglobin, creatine kinase-MB (CK-MB), and troponin-I. It has also been used as an interfering agent to test the effectiveness of the Heparin Red kit in the detection of various heparins.

Bilirubin is an active oxidative DNA cleaving agent as well as an effective antioxidant agent, a hydroxyl radical quencher. This bile pigment has both antioxidant and toxic properties. It is a natural inhibitor of vascular smooth muscle cell proliferation (VSMCs). It displays anti-inflammatory and anti-proliferative properties when used as a therapeutic agent in lung/vascular diseases. Serum bilirubin concentration slightly above the normal levels have shown a lesser incidence of heart disease. It is a potential therapeutic agent in heart transplantation and T-cell mediated immune disorders.

Well over 99% of total bilirubin is transported as a conjugate with albumin. Abnormally high levels of bilirubin can cause severe neurological damage, but mildly elevated levels are linked to protection from oxidative stress.

λ_max. ∼453 nm, mol. absorption >56100 (chloroform)