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.
Healthy newborns — especially those who are premature — often develop 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 clear up on their own. But because high bilirubin levels can cause health problems like 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 also can be due to hemolytic disease. This condition happens when there is an incompatibility between the blood types of the mother and baby, which leads to a faster 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 from conditions, such as liver disease, bile duct blockage, or thyroid disease.
No special preparations are needed for this test. Having your child wear a T-shirt or short-sleeved shirt on the day of the test can make things faster and easier for the technician who will be drawing the blood.
A health professional will usually draw the blood from a vein. For an infant, the blood may be obtained by puncturing the heel with a small needle (lancet). If the blood is being drawn from a vein, the skin surface is cleaned with antiseptic, and an elastic band (tourniquet) is placed around the upper arm to apply pressure and cause the veins to swell with blood. A needle is inserted into a vein (usually in the arm inside of the elbow or on the back of the hand) and blood is withdrawn and collected in a vial or syringe.
After the procedure, the elastic band is removed. Once the blood has been collected, the needle is removed and the area is covered with cotton or a bandage to stop the bleeding. Collecting blood for this test will only take a few minutes.
Either method (heel or vein withdrawal) of collecting a sample of blood is only temporarily uncomfortable and can feel like a quick pinprick. Afterward, there may be some mild bruising, which should go away in a few days.
The blood sample will be processed by a machine. The results are generally available after a few hours or the next day.
Bilirubin levels are evaluated according to your child's age.
The bilirubin test is considered a safe procedure. However, as with many medical tests, some problems can occur with having blood drawn, such as:
Having a blood test is relatively painless. Still, many kids are afraid of needles. Explaining the test in terms your child can understand might help ease some of the fear.
Allow your child to ask the technician any questions he or she might have. Tell your child to try to relax and stay still during the procedure, as tensing muscles and moving can make it harder and more painful to draw blood. It also may help if your child looks away when the needle is being inserted into the skin.
If you have questions about the bilirubin test, speak with your doctor. You also can talk to the technician before the procedure.
Reviewed by: Yamini Durani, MD
Date reviewed: July 2014
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