Also known as:Total Bilirubin; TBIL; Neonatal Bilirubin; Direct Bilirubin; Conjugated Bilirubin; Indirect Bilirubin; Unconjugated Bilirubin
Formal name:Bilirubin - blood
Related tests:Liver Panel; GGT; ALP; AST; ALT; Hepatitis A; Hepatitis B; Hepatitis C; Complete Blood Count; Urinalysis; Direct Antiglobulin Test; Haptoglobin; Reticulocyte Count
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Why Get Tested?
To screen for or monitor liver disorders or hemolytic anemia; to monitor neonatal jaundice
When to Get Tested?
When you have signs or symptoms of liver damage, liver disease, bile duct blockage, hemolytic anemia, or a liver-related metabolic problem, or if a newborn has jaundice
In adults, a blood sample drawn from a vein in the arm; in newborns, a blood sample from a heelstick; non-invasive technology is available in some healthcare facilities that will measure bilirubin by using an instrument placed on the skin (transcutaneous bilirubin meter)
Test Preparation Needed?
You may need to fast (nothing but water) for several hours before the test; fasting requirements vary by laboratory; ask your lab or healthcare provider for instructions.
How is it used?
A bilirubin test is used to detect an increased level in the blood. It may be used to help determine the cause of jaundice and/or help diagnose conditions such as liver disease, hemolytic anemia, and blockage of the bile ducts.
Bilirubin is an orange-yellow pigment, a waste product primarily produced by the normal breakdown of heme. Heme is a component of hemoglobin, which is found in red blood cells (RBCs). Bilirubin is ultimately processed by the liver to allow its elimination from the body. Any condition that accelerates the breakdown of RBCs or affects the processing and elimination of bilirubin may cause an elevated blood level.
Two forms of bilirubin can be measured or estimated by laboratory tests:
- unconjugated bilirubin–when heme is released from hemoglobin, it is converted to unconjugated bilirubin. It is carried by proteins to the liver. Small amounts may be present in the blood.
- conjugated bilirubin–formed in the liver when sugars are attached (conjugated) to bilirubin. It enters the bile and passes from the liver to the small intestines and is eventually eliminated in the stool. Normally, no conjugated bilirubin is present in the blood.
Usually, a chemical test is used to first measure the total bilirubin level (unconjugated plus conjugated bilirubin). If the total bilirubin level is increased, the laboratory can use a second chemical test to detect water-soluble forms of bilirubin, called "direct" bilirubin. The direct bilirubin test provides an estimate of the amount of conjugated bilirubin present. Subtracting direct bilirubin level from the total bilirubin level helps estimate the "indirect" level of unconjugated bilirubin. The pattern of bilirubin test results can give the healthcare provider information regarding the condition that may be present.
In adults and older children, bilirubin is measured to:
- Diagnose and/or monitor diseases of the liver and bile duct (e.g., cirrhosis, hepatitis, or gallstones)
- Evaluate people with sickle cell disease or other causes of hemolytic anemia; these people may have episodes called crises when excessive RBC destruction increases bilirubin levels.
In newborns with jaundice, bilirubin is used to distinguish the causes of jaundice.
- In both physiologic jaundice of the newborn and hemolytic disease of the newborn, only unconjugated (indirect) bilirubin is increased.
- In much less common cases, damage to the newborn's liver from neonatal hepatitis and biliary atresia will increase conjugated (direct) bilirubin concentrations as well, often providing the first evidence that one of these less common conditions is present.
It is important that an elevated level of bilirubin in a newborn be identified and quickly treated because excessive unconjugated bilirubin damages developing brain cells. The consequences of this damage include mental retardation, learning and developmental disabilities, hearing loss, eye movement problems, and death.
When is it ordered?
A health practitioner usually orders a bilirubin test in conjunction with other laboratory tests (alkaline phosphatase, aspartate aminotransferase, alanine aminotransferase) when someone shows signs of abnormal liver function. A bilirubin level may be ordered when a person:
- Shows evidence of jaundice
- Has a history of drinking excessive amounts of alcohol
- Has suspected drug toxicity
- Has been exposed to hepatitis-causing viruses
Other symptoms that may be present include:
- Dark, amber-colored urine
- Abdominal pain and/or swelling
- Fatigue and general malaise that often accompany chronic liver disease
Measuring and monitoring bilirubin in newborns with jaundice is considered standard medical care.
Tests for bilirubin may also be ordered when someone is suspected of having (or known to have) hemolytic anemia as a cause of anemia. In this case, it is often ordered along with other tests used to evaluate hemolysis, such as complete blood count, reticulocyte count, haptoglobin, and LDH.
What does the test result mean?
Adults and children
Increased total bilirubin that is mainly unconjugated (indirect) bilirubin may be a result of:
- Hemolytic or pernicious anemia
- Transfusion reaction
- A relatively common inherited condition called Gilbert syndrome, due to low levels of the enzyme that produces conjugated bilirubin
If conjugated (direct) bilirubin is elevated more than unconjugated (indirect) bilirubin, there typically is a problem associated with decreased elimination of bilirubin by the liver cells. Some conditions that may cause this include:
- Viral hepatitis
- Drug reactions
- Alcoholic liver disease
Conjugated (direct) bilirubin is also elevated more than unconjugated (indirect) bilirubin when there is blockage of the bile ducts. This may occur, for example, with:
- Gallstones present in the bile ducts
- Scarring of the bile ducts
Rare inherited disorders that cause abnormal bilirubin metabolism such as Rotor, Dubin-Johnson, and Crigler-Najjar syndromes, may also cause increased levels of bilirubin.
Low levels of bilirubin are generally not concerning and are not monitored.
An elevated bilirubin level in a newborn may be temporary and resolve itself within a few days to two weeks. However, if the bilirubin level is above a critical threshold or increases rapidly, an investigation of the cause is needed so appropriate treatment can be initiated. Increased bilirubin concentrations may result from the accelerated breakdown of red blood cells due to:
- Blood type incompatibility between the mother and her newborn
- Certain congenital infections
- Lack of oxygen (hypoxia)
- Diseases that can affect the liver
In most of these conditions, only unconjugated (indirect) bilirubin is increased. An elevated conjugated (direct) bilirubin is seen in the rare conditions of biliary atresia and neonatal hepatitis. Biliary atresia requires surgical intervention to prevent liver damage.
Is there anything else I should know?
Though unconjugated bilirubin may be toxic to brain development in newborns (up to 2-4 weeks of age), it does not pose the same threat to older children and adults. In older children and adults, the "blood-brain barrier" is more developed and prevents bilirubin from gaining access to brain cells. Nevertheless, elevated bilirubin strongly suggests that a medical condition is present that must be evaluated and treated.
Bilirubin is not normally present in the urine. However, conjugated bilirubin is water-soluble and may be eliminated from the body through the urine if it cannot pass into the bile. Measurable bilirubin in the urine usually indicates blockage of liver or bile ducts, hepatitis, or some other form of liver damage and may be detectable early in disease; for this reason, bilirubin testing is integrated into common dipstick testing used for routine urinalysis.
Bilirubin concentrations tend to be slightly higher in males than females. African Americans routinely show lower bilirubin concentrations than non-African Americans. Strenuous exercise may increase bilirubin levels.
Drugs that can decrease total bilirubin include barbiturates, caffeine, penicillin, and high doses of salicylates. The drug atazanavir increases unconjugated (indirect) bilirubin.
What is being tested?
Bilirubin is an orange-yellow pigment, a waste product primarily produced by the normal breakdown of heme. Heme is a component of hemoglobin, which is found in red blood cells (RBCs). Bilirubin is ultimately processed by the liver to allow its elimination from the body. This test measures the amount of bilirubin in the blood to evaluate a person's liver function or to help diagnose anemias caused by RBC destruction (hemolytic anemia).
RBCs normally degrade after about 120 days in circulation. As heme is released from hemoglobin, it is converted to bilirubin. This form of bilirubin is also called unconjugated bilirubin. Unconjugated bilirubin is carried by proteins to the liver; there, sugars are attached (conjugated) to bilirubin to form conjugated bilirubin. Conjugated bilirubin enters the bile and passes from the liver to the small intestines; there, it is further broken down by bacteria and eventually eliminated in the stool. Thus, the breakdown products of bilirubin give stool its characteristic brown color.
A small amount (approximately 250 to 350 milligrams) of bilirubin is produced daily in a normal, healthy adult. Most (85%) of bilirubin is derived from damaged or degraded RBCs, with the remaining amount derived from the bone marrow or liver. Normally, small amounts of unconjugated bilirubin are released into the blood, but virtually no conjugated bilirubin is present. Both forms can be measured or estimated by laboratory tests, and a total bilirubin result (a sum of these) may also be reported.
If the bilirubin level increases in the blood, a person may appear jaundiced, with a yellowing of the skin and/or whites of the eyes. The pattern of bilirubin test results can give the health practitioner information regarding the condition that may be present. For example, unconjugated bilirubin may be increased when there is an unusual amount of RBC destruction (hemolysis) or when the liver is unable to process bilirubin (i.e., with liver diseases such as cirrhosis or inherited problems). Conversely, conjugated bilirubin can increase when the liver is able to process bilirubin but is not able to pass the conjugated bilirubin to the bile for removal; when this happens, the cause is often acute hepatitis or blockage of the bile ducts.
Increased total and unconjugated bilirubin levels are relatively common in newborns in the first few days after birth. This finding is called "physiologic jaundice of the newborn" and occurs because the newborn's liver is not mature enough to process bilirubin yet. Usually, physiologic jaundice of the newborn resolves itself within a few days. However, in hemolytic disease of the newborn, RBCs may be destroyed because of blood incompatibilities between the baby and the mother; in these cases, treatment may be required because high levels of unconjugated bilirubin can damage the newborn's brain.
A rare (about 1 in 10,000 births) but life-threatening congenital condition called biliary atresia can cause increased total and conjugated bilirubin levels in newborns. This condition must be quickly detected and treated, usually with surgery, to prevent serious liver damage that may require liver transplantation within the first few years of life. Some children may require liver transplantation despite early surgical treatment.
How is the sample collected for testing?
In adults, blood is typically collected from a vein in the arm using a needle. In newborns, blood is often collected from a heelstick. Heelstick is a technique that uses a small, sharp blade to cut the skin on the infant's heel so that a few drops of blood can be collected in a small tube. Non-invasive technology that measures bilirubin through the skin is available in some healthcare facilities; this instrument is called a transcutaneous bilirubin meter.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
You may need to fast (nothing but water) for several hours before the test; fasting requirements vary by laboratory. Ask your lab or healthcare provider for instructions.
- Are some people more at genetic risk of abnormal bilirubin levels?
Several inherited chronic conditions increase bilirubin levels in the blood and include Gilbert syndrome, Dubin-Johnson syndrome, Rotor syndrome, and Crigler-Najjar syndrome. The first three are usually mild, chronic conditions that can be aggravated under certain conditions but in general cause no significant health problems. For example, Gilbert syndrome is very common; about 1 in every 6 people has this genetic abnormality, but usually people with Gilbert syndrome do not have elevated bilirubin. Crigler-Najjar syndrome is the most serious inherited condition listed; this disorder is relatively rare, and some people with it may die.
- How do you treat abnormal bilirubin levels and/or jaundice?
Treatment depends on the cause of the jaundice. In newborns, phototherapy (special light therapy), blood exchange transfusion, and/or certain drugs may be used to reduce the bilirubin level. In Gilbert, Rotor, and Dubin-Johnson syndromes, no treatment is usually necessary. Crigler-Najjar syndrome may respond to certain enzyme drug therapy or may require a liver transplant. Jaundice caused by an obstruction is often resolved by surgery. Jaundice due to cirrhosis is a result of long-term liver damage and does not respond well to any type of therapy other than liver transplantation.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
Descriptions of clinical laboratory tests were originally prepared for use on Lab Tests Online, an award-winning patient education website on clinical laboratory testing. Lab Tests Online is produced by the American Association for Clinical Chemistry (AACC), a global scientific and medical professional organization dedicated to clinical laboratory science and its application to healthcare. The Lab Tests Online website is developed in collaboration with other laboratory professional societies and is funded in part through corporate sponsorships.