Bilirubin, Indirect Unit Converter

Indirect bilirubin (also called unconjugated bilirubin) is a yellow-orange pigment formed when red blood cells are broken down. It is the form of bilirubin that has not yet been processed by the liver.

Because indirect bilirubin is not water-soluble, it must bind to albumin (a blood protein) to travel through the bloodstream to the liver. There, it undergoes conjugation, which converts it to direct (conjugated) bilirubin that can be excreted in bile.

Under normal conditions, indirect bilirubin makes up about 70-85% of total bilirubin in the blood. Indirect bilirubin is calculated by subtracting direct bilirubin from total bilirubin.

Indirect bilirubin is produced primarily in the spleen and other parts of the reticuloendothelial system when aging red blood cells are broken down. The hemoglobin released from these cells is converted first to heme, then to biliverdin, and finally to unconjugated bilirubin.