Bilirubin is a brownish yellow substance found in bile. Bilirubin is produced when the liver breaks down hemoglobin, the oxygen-carrying substance in red blood cells. Bilirubin is then removed from the body through the stool (feces) and gives stool its normal brown color.

Bilirubin circulates in the bloodstream in two forms:

• Indirect (or unconjugated) bilirubin. This form of bilirubin does not dissolve in water (it is insoluble). Indirect bilirubin travels through the bloodstream to the liver, where it is changed into a soluble form.
• Direct (or conjugated) bilirubin. After indirect bilirubin has been changed by the liver to a form that dissolves in water (soluble), it is called direct or conjugated bilirubin.

Total bilirubin (direct plus indirect) is often measured by itself. If the total bilirubin result is abnormally high, the direct and indirect forms of bilirubin are then usually measured separately to provide more information.

The most obvious symptom of high bilirubin levels is jaundice, a condition in which the skin and whites of the eyes appear yellow. Jaundice is caused by the buildup of bilirubin in the blood and skin due to liver disease hepatitis, blood disorders hemolytic anemia, or blockage of the tubes (bile ducts) that allow bile to pass from the liver to the small intestine.

Excessive buildup of bilirubin in a newborn baby sometimes causes brain damage and even death. Therefore, some babies who develop jaundice may be treated with special lights or a blood transfusion to reduce their bilirubin levels.

This test is done on a blood sample taken from a vein. In a newborn baby, the blood sample is usually taken from the heel (heel stick).

Bilirubin
Results

Normal

Normal values may vary from lab to lab.

Greater than normal values may mean

• High levels of bilirubin in the blood may occur because either too much bilirubin is being produced or not enough bilirubin is being eliminated.
• Decreased elimination of bilirubin can be caused by some infections (such as an infected gallbladder, or cholecystitis) or by certain inherited enzyme deficiencies. Gilbert's syndrome, an inherited condition that affects how the liver processes bilirubin, is a common cause of increased blood levels of bilirubin. Although jaundice may occur in some people with Gilbert's syndrome, the condition usually is not harm ful.
• Decreased elimination of bilirubin may result from liver damage (caused by hepatitis, cirrhosis, or mononucleosis, digest ive system problems that result in excessive reabsorption of bilirubin, or blockage of the bile ducts (such as from gallstones or pancreatic cancer).
• Because their livers are immature, premature infants may not be able to eliminate bilirubin properly from the blood and are more likely to develop jaundice than full-term babies.
• Elevated bilirubin levels may be caused by rapid destruction of red blood cells in the blood, such as from sickle cell disease or an allergic reaction to blood received during a transfusion (called a transfusion reaction).

The amounts of both direct and indirect bilirubin can help determine the cause of the excess bilirubin:

• Excessive breakdown of red blood cells increases indirect bilirubin levels more than direct bilirubin levels.
• Blockage of the bile ducts (such from a gallstones or pancreatic cancer) tends to increase the amount of direct bilirubin more than indirect bilirubin.
• In severe liver damage, direct bilirubin may return to normal or almost-normal levels, but indirect bilirubin levels will remain high.