Bilirubin is a substance produced when old red blood cells are broken down. It mainly exists in two forms in the blood, unconjugated or indirect bilirubin, and conjugated or direct bilirubin. Typically, your liver removes most of the substance from your body. If your liver is damaged or red blood cells are being destroyed faster than normal, excess bilirubin is released into the bloodstream, which can cause your skin and eyes to turn yellow. If jaundice is suspected, a bilirubin blood test can help determine if there is liver disease or hemolysis.