A bilirubin test measures the amount of bilirubin in a blood sample. Bilirubin is a brownish yellow substance found in bile. It is produced when the liver breaks down old red blood cells. Bilirubin is then removed from the body through the stool (feces) and gives stool its normal color.
Bilirubin circulates in the bloodstream in two forms:
- Indirect (or unconjugated) bilirubin.
This form doesn't 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).
- Direct (or conjugated) bilirubin.
Direct bilirubin dissolves in water. (It is soluble.) It's made by the liver from indirect bilirubin.
Total bilirubin and direct bilirubin levels are measured directly in the blood. Indirect bilirubin levels are derived from the total and direct bilirubin measurements.
When bilirubin levels are high, the skin and whites of the eyes may look yellow (jaundice). Jaundice may be caused by 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.
Mild jaundice in newborns usually doesn't cause problems. But too much bilirubin (hyperbilirubinemia) in a newborn baby can cause brain damage (kernicterus) and other serious problems. So some babies who develop jaundice may need treatment to lower their bilirubin levels.
Why It Is Done
The bilirubin test is used to:
- Check liver function and watch for signs of liver disease, such as hepatitis or cirrhosis, or the effects of medicines that can damage the liver.
- Find out if something is blocking the bile ducts. This may occur if gallstones, tumors of the pancreas, or other conditions are present.
- Diagnose conditions that cause increased destruction of red blood cells, such as hemolytic anemia or hemolytic disease of the newborn.
- Help make decisions about whether newborn babies with neonatal jaundice need treatment. These babies may need treatment with special lights, called phototherapy. In rare cases, blood transfusions may be needed.
How To Prepare
- Adults should not eat or drink for 4 hours before the test.
- For children, there's generally nothing you have to do before this test, unless your doctor tells you to.
How It Is Done
Blood sample from a heel stick
For a heel stick blood sample, several drops of blood are collected from the baby's heel. The skin of the heel is first cleaned with alcohol and then punctured with a small sterile lancet. Several drops of blood are collected in a small tube. When enough blood has been collected, a gauze pad or cotton ball is placed over the puncture site. Pressure is maintained on the puncture site briefly. Then a small bandage is usually applied.
Instead of the standard heel stick, some hospitals may use a device called a transcutaneous bilirubin meter to check a newborn's bilirubin level. This small handheld device measures bilirubin levels when it is placed gently against the skin. With this device, there may be no need to puncture the baby's skin. This is a screening test, and a blood sample will be needed if the baby's bilirubin level is high.
Blood sample from a vein
A health professional uses a needle to take a blood sample, usually from the arm.
How long the test takes
The test will take a few minutes.
How It Feels
Blood sample from a heel stick
A brief pain, like a sting or a pinch, is usually felt when the lancet punctures the skin. A baby may feel a little discomfort with the skin puncture.
Blood sample from a vein
When a blood sample is taken, you may feel nothing at all from the needle. Or you might feel a quick sting or pinch.
There is very little risk of a problem from a heel stick. Your baby may get a small bruise at the puncture site.
There is very little chance of having a problem from this test. When a blood sample is taken, a small bruise may form at the site.
The results are usually available in 1 to 2 hours.
Normal values in adults
Each lab has a different range for what's normal. Your lab report should show the range that your lab uses for each test. The normal range is just a guide. Your doctor will also look at your results based on your age, health, and other factors. A value that isn't in the normal range may still be normal for you.
- Results that show slightly high bilirubin levels may be nothing to worry about. It could be caused by certain inherited diseases, such as Gilbert's syndrome. This is a condition that affects how the liver processes bilirubin. Some people with this problem get jaundice, but it's not harmful.
- High levels of bilirubin in the blood may be caused by:
- Some infections, such as an infected gallbladder, or cholecystitis.
- Diseases that cause liver damage, such as hepatitis, cirrhosis, or mononucleosis.
- Diseases that cause blockage of the bile ducts, such as gallstones or cancer of the pancreas.
- 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).
- Medicines that may increase bilirubin levels. This includes many antibiotics, some types of birth control pills, diazepam (Valium), flurazepam, indomethacin (Indocin), and phenytoin (Dilantin).
Low levels of bilirubin in the blood may be caused by:
- Medicines that may decrease bilirubin levels. This includes vitamin C, phenobarbital, and theophylline.
Normal values in newborns
Normal values in newborns depend on the age of the baby in hours and whether the baby was premature or full term. Normal values may vary from lab to lab.