Bilirubin is a yellow pigment that’s in everyone’s blood and stool. A bilirubin blood test determines the levels of bilirubin in the body.

Sometimes the liver can’t process the bilirubin in the body. This can be due to an excess of bilirubin, an obstruction, or inflammation of the liver.

When your body has too much bilirubin, your skin and the whites of your eyes will start to yellow. This condition is called jaundice.

A bilirubin test will help determine if you have any of these conditions.

Bilirubin is made in the body when the hemoglobin protein in old red blood cells is broken down. The breakdown of old cells is a normal, healthy process.

After circulating in your blood, bilirubin then travels to your liver.

In the liver, bilirubin is processed, mixed into bile, and then excreted into the bile ducts and stored in your gallbladder.

Eventually, the bile is released into the small intestine to help digest fats. It’s ultimately excreted within your stool.

Bilirubin attached by the liver to glucuronic acid, a glucose-derived acid, is called direct, or conjugated, bilirubin. Bilirubin not attached to glucuronic acid is called indirect, or unconjugated, bilirubin. All the bilirubin in your blood together is called total bilirubin.

A comprehensive bilirubin blood test will get an accurate count of all three bilirubin levels in your blood: direct, indirect, and total.

In both adults and children, symptoms related to high bilirubin can involve jaundice, a yellowing of the skin or eyes, fatigue, itchy skin, dark urine, and low appetite.

If bilirubin isn’t being attached to the glucose-derived acid (conjugated) in the liver or isn’t being adequately removed from the blood, it can mean that there is damage to your liver.

Testing for bilirubin in the blood is therefore a good way of testing for liver damage.

Mild jaundice in newborns can either be due to normal changes in the metabolism of bilirubin, or it can be the first sign of a medical problem.

If the level at birth is too high, an infant’s blood may be tested several times in the first few days of their life to monitor liver function. Jaundice in a newborn can be very serious and life-threatening if left untreated.

Another reason for high bilirubin levels could be that more red blood cells are being destroyed than normal. This is called hemolysis.

Sometimes bilirubin is measured as part of a “panel” of tests. Often, the liver is evaluated with a group of tests that also include:

A small amount of your blood is needed to perform this test. The blood sample is obtained through venipuncture: A needle is inserted into a vein through the skin in your arm or hand, and a small amount of blood is collected in a test tube.

For this test, you will need to not eat or drink anything other than water for four hours before you have the test performed. You can drink your usual amount of water before going to the laboratory or collection site.

You may have to stop taking certain medications before the test is performed, but only if your doctor tells you to do so.

Examples of drugs that can affect bilirubin levels include antibiotics like penicillin G, sedatives like phenobarbital, diuretics like furosemide (Lasix), and asthma medications like theophylline.

There are many other drugs that can influence bilirubin levels. Talk to your doctor before your test to see if you should stop or continue taking medication.

When the blood is collected, you may briefly feel moderate pain or a mild pinching sensation. After the needle is taken out, you may feel a throbbing sensation.

You’ll be instructed to apply pressure to the site where the needle entered your skin. A bandage will be placed over the site. Keep this bandage on for at least 10 to 20 minutes.

You should avoid using that arm for heavy lifting for the rest of the day.

There are some very rare risks to taking a blood sample:

  • lightheadedness or fainting
  • hematoma, a bruise where blood accumulates under the skin
  • infection, usually prevented by the skin being cleaned before the needle is inserted
  • excessive bleeding, or bleeding for a long period afterward, which may indicate a more serious bleeding condition and should be reported to your doctor

In an older child or adult, normal values of direct bilirubin are from 0–0.4 milligrams per deciliter (mg/dL). Normal values of total bilirubin are from 0.3–1.0 mg/dL.

The indirect bilirubin level in the bloodstream is the total bilirubin minus the direct bilirubin levels in the bloodstream. Additionally, normal reference ranges may vary from lab to lab.

In a newborn, higher bilirubin is normal due to the stress of birth. Normal indirect bilirubin would be under 5.2 mg/dL within the first 24 hours of birth. But many newborns have some kind of jaundice and bilirubin levels that rise above 5 mg/dL within the first few days after birth.

Your doctor may want to perform further blood tests or an ultrasound if high levels of bilirubin are detected in your blood. In an adult, high bilirubin may be due to problems with the liver, bile ducts, or gallbladder. Examples include:

High bilirubin may also be due to problems in the blood instead of problems in the liver. Blood cells breaking down too fast can be caused by:

  • Hemolytic anemia: This occurs when too many blood cells are being destroyed from an autoimmune disease, genetic defect, drug toxicity, or infection, and the liver is unable to metabolize the amount of indirect bilirubin in the body.
  • Transfusion reaction: This occurs when your immune system attacks blood that was given to you through a transfusion.

In an infant, high (usually indirect) bilirubin and jaundice can be very dangerous and may be caused by several factors. There are three common types:

  • physiological jaundice: at two to four days after birth, caused by a brief delay in the functioning of the liver and usually not serious
  • breastfeeding jaundice: during the first week of life, caused by a baby not nursing well or low milk supply in the mother
  • breast milk jaundice: after two to three weeks of life, caused by the processing of some substances in breast milk

All of these can be easily treated and are usually harmless if treated. Some more serious conditions that cause high bilirubin and jaundice in an infant include:

  • abnormal blood cell shapes, such as sickle cell anemia
  • blood-type mismatch between infant and mother, leading to severe breakdown of the baby’s red blood cells, called erythroblastosis fetalis
  • lack of certain important proteins due to genetic defects
  • bruising due to a difficult delivery
  • high levels of red blood cells due to small size, prematurity
  • infections

If your blood tests show abnormally high levels of bilirubin, your doctor may order more tests to determine the underlying cause.

Once your doctor has determined a cause of high bilirubin levels, you may need to take more bilirubin blood tests to monitor the effectiveness of your treatment.

If your doctor thinks your liver or gallbladder might not be functioning properly, they may order imaging tests to ensure there are no structural abnormalities.