
What It Is
A bilirubin test measures the level of bilirubin (a byproduct of the normal breakdown of old red blood cells) in the blood. Normally, bilirubin passes through the liver and is excreted through the intestines as bile (a yellowish colored fluid that helps in the digestion of fats). But if that doesn't happen due to a liver disease or other health problem, bilirubin can build up in the blood, causing the skin to take on the yellow discoloration known as jaundice.
Bilirubin exists in two forms in the body: indirect (unconjugated) and direct (conjugated). Indirect bilirubin, which doesn't dissolve in water, must travel to the liver to be changed into the soluble form, direct bilirubin.
Why It's Done
Healthy newborns — especially those who are premature — are commonly susceptible to jaundice because their immature livers are slow to process bilirubin. Jaundice is also fairly common among breastfeeding babies who aren't getting enough milk, or those whose mothers naturally produce substances that raise bilirubin levels.
Most mild cases resolve on their own. But because high bilirubin levels can cause hearing loss and brain damage in babies, the American Academy of Pediatrics (AAP) recommends that all infants be examined for jaundice soon after birth. If the doctor feels that the baby is more jaundiced than would be expected, a blood test is done to determine the exact level of bilirubin in the blood.
Babies with high levels may need phototherapy (treatment with a special light that makes bilirubin easier for the liver to process), or in rare cases, a procedure called an exchange transfusion in which the infant's bilirubin level is brought down by removing bilirubin-rich blood from the baby and replacing it with blood that contains normal levels of bilirubin.
High bilirubin levels in infants may also be the result of hemolytic disease, a condition that occurs when there is an incompatibility between the blood types of the mother and baby leading to more rapid breakdown of the infant's red blood cells.
Doctors may order a bilirubin test in other infants or older children who have have developed jaundice due to other conditions, such as liver disease, bile duct blockage, or thyroid disease.
Preparation
No special preparations are needed for this test. Having your child wear a short-sleeve shirt on the day of the test can make things faster and easier for the technician who will be drawing the blood.