Bilirubin diglucuronide is a metabolite of bilirubin made by conjugating it with two molecules of glucuronic acid (Figure 21.31). This reaction, which helps make the relatively insoluble bilirubin much more water soluble, occurs in the liver. After conversion, bilirubin diglucuronide is secreted into the bile and is ultimately excreted via the intestine. The pathway of heme breakdown in the body is as follows:

Heme -> Biliverdin -> Bilirubin -> (passage through blood to liver as bilirubin-albumin complex) -> Bilirubin diglucuronide -> excretion.