Bilirubin

Bilirubin is an orange-yellow pigment found in bile. Red blood cells (RBCs) normally degrade after 120 days in the circulation. At this time, a component of the RBCs, hemoglobin (the red-colored pigment of red blood cells that carries oxygen to tissues), breaks down into unconjugated bilirubin. Approximately 250 to 350 mg of bilirubin is produced daily in a normal, healthy adult, of which 85% is derived from damaged or old red cells that have died, with the remaining amount from the bone marrow or liver.

Unconjugated bilirubin is carried to the liver, where sugars are attached to it to make it water soluble, producing conjugated bilirubin. This conjugated bilirubin is passed to the bile by the liver and is further broken down by bacteria in the small intestines and eventually excreted in the feces. The breakdown products of bilirubin give feces its characteristic brown color. If bilirubin levels increase in the blood, the appearance of jaundice becomes more evident. Normally, almost all bilirubin in the blood is unconjugated.

In newborns, blood is often collected from a heelstick, a technique that uses a small, sharp blade to cut the skin on the infant’s heel and collect a few drops of blood into a small tube. For adults, blood is typically collected by needle from a vein. Non-invasive technology is available in some health care facilities that will measure bilirubin by using an instrument placed on the skin (transcutaneous bilirubin meter).

No test preparation is needed.