Bilirubin is the main bile pigment that is formed from the breakdown of heme in red blood cells. The broken down heme travels to the liver, where it is secreted into the bile by the liver. Normally, a small amount of bilirubin circulates in the blood. Serum bilirubin is considered a true test of liver function, as it reflects the liver's ability to take up, process, and secrete bilirubin into the bile.
Bilirubin is a brownish-yellow pigment that is found in bile, which is a liquid secreted by the liver that allows the body to digest fats. There are two forms of bilirubin, direct and indirect. Direct bilirubin is often referred to as conjugated bilirubin, while indirect bilirubin is known as unconjugated bilirubin. The difference between direct and indirect bilirubin is that direct bilirubin is water-soluble and indirect bilirubin is not. This means that direct bilirubin is able to be dissolved in water.
Direct bilirubin production is the final step in a complex chain of events that occur as the body rids itself of the waste left over from old red blood cells. During the first stage, indirect bilirubin is produced within certain types of cells that reside in bone marrow, the liver, and the spleen. This happens as red-blood cells reach the end of their life cycles and begin to break down into their component parts. One of these component parts, heme, a reddish pigment, is further broken down to make indirect bilirubin.
Newly formed indirect bilirubin is then carried into the liver via water-soluble proteins known as albumin. In the liver, indirect bilirubin becomes water-soluble when it reacts with a sugar based compound known as glucuronic acid. Once this occurs, direct bilirubin is formed. As soon as it becomes water soluble, the body prepares to remove it from the body.
Bilirubin production and excretion follows a specific pathway. When the reticuloendothelial system breaks down old red blood cells, bilirubin is one of the waste products. This "free bilirubin", is in a lipid-soluble form that must be made water-soluble to be excreted. The free, or unconjugated, bilirubin is carried by albumin to the liver, where it is converted or conjugated and made water soluble. Once it is conjugated into a water-soluble form, bilirubin can be excreted in the urine. An enzyme, glucuronyl transferase, is necessary for the conjugation of bilirubin. Either a lack of this enzyme, or the presence of drugs that interfere with glucuronyl transferase, impairs the liver's ability to conjugate bilirubin. Because the bilirubin is chemically different after it goes through the conjugation process in the liver, lab tests can differentiate between the unconjugated or indirect bilirubin and conjugated or direct bilirubin. The terms "direct" and "indirect" reflect the way the two types of bilirubin react to certain dyes. Conjugated bilirubin is water-soluble and reacts directly when dyes are added to the blood specimen. The non-water soluble, free bilirubin does not react to the reagents until alcohol is added to the solution. Therefore, the measurement of this type of bilirubin is indirect. Test results may be listed as "BU" for unconjugated bilirubin and "BC" for conjugated bilirubin. Total bilirubin measures both BU and BC.
Bilirubin concentrations are elevated in the blood either by increased production, decreased conjugation, decreased secretion by the liver, or blockage of the bile ducts. In cases of increased production, or decreased conjugation, the unconjugated or indirect form of bilirubin will be elevated. Unconjugated hyperbilirubinemia is caused by accelerated erythrocyte hemolysis in the newborn (erythroblastosis fetalis), absence of glucuronyl transferase, or hepatocellular disease. Conjugated hyperbilirubinemia is caused by obstruction of the biliary ducts, as with gallstones or hepatocellular diseases such as cirrhosis or hepatitis. Elevated serum bilirubin test results may also be caused by the effects of many different drugs, including antibiotics, barbiturates, steroids, or oral contraceptives. In chronic acquired liver diseases, the serum bilirubin concentration is usually normal until a significant amount of liver damage has occurred and cirrhosis is present. In acute liver disease, the bilirubin is usually increased in relation to the severity of the acute process.
Almost all of the bilirubin produced is excreted as one of the components of bile salts. Bilirubin is the pigment that gives bile its characteristic bright greenish yellow color. When the bile salts reach the intestine via the common bile duct, the bilirubin is acted on by bacteria to form chemical compounds called urobilinogens. Most of the urobilinogen is excreted in the feces; some is reabsorbed and goes through the liver again and a small amount is excreted in the urine. Urobilinogen gives feces their dark color. An absence of bilirubin in the intestine, such as may occur with bile duct obstruction, blocks the conversion of bilirubin to urobilinogen, resulting in clay-colored stools.
The following is a review of the normal pathway for bilirubin production and excretion and its relationship to laboratory assessment of liver function:
Step 1: Red blood cells are broken down by the reticuloendothelial system and unconjugated bilirubin in the bloodstream is carried by albumin to the liver. This is known as "pre-hepatic," "free," "unconjugated," or"indirect bilirubin" (normal value = 0.1 - 1.0 mg/dl)
Step 2: The liver converts or conjugates bilirubin and makes it water-soluble. This is known as "posthepatic", "conjugated" or "direct" bilirubin (normal value = 0.0 - 0.4 mg/dl)
Step 3: Conjugated bilirubin is excreted via bile salts to intestine. Bacteria in the intestine break down bilirubin to urobilinogen for excretion in the feces (normal value for fecal urobilinogen = 40 - 280 mg/day)
Bilirubin (formerly referred to as hematoidin) is the yellow breakdown product of normal heme catabolism. Heme is found in hemoglobin, a principal component of red blood cells. Bilirubin is excreted in bile and urine, and elevated levels may indicate certain diseases. It is responsible for the yellow color of bruises, the yellow color of urine (via its reduced breakdown product, urobilin), the brown color of feces (via its conversion to stercobilin), and the yellow discoloration in jaundice. It has also been found in plants.
Structure of Bilirubin
Bilirubin consists of an open chain of four pyrrole-like rings (tetrapyrrole). In heme, by contrast, these four rings are connected into a larger ring, called a porphyrin ring.
Bilirubin is very similar to the pigment phycobilin used by certain algae to capture light energy, and to the pigment phytochrome used by plants to sense light. All of these contain an open chain of four pyrrolic rings.
Like these other pigments, some of the double-bonds in bilirubin isomerize when exposed to light. This is used in the phototherapy of jaundiced newborns: the E,Z-isomers of bilirubin formed upon light exposure are more soluble than the unilluminated Z,Z-isomer, as the possibility of intramolecular hydrogen bonding is removed. This allows the excretion of unconjugated bilirubin in bile.
Some textbooks and research articles show the incorrect geometric isomer of bilirubin. The naturally occurring isomer is the Z,Z-isomer.
Bilirubin is created by the activity of biliverdin reductase on biliverdin, a green tetrapyrrolic bile pigment that is also a product of heme catabolism. Bilirubin, when oxidized, reverts to become biliverdin once again. This cycle, in addition to the demonstration of the potent antioxidant activity of bilirubin, has led to the hypothesis that bilirubin's main physiologic role is as a cellular antioxidant.
Erythrocytes (red blood cells) generated in the bone marrow are disposed of in the spleen when they get old or damaged. This releases hemoglobin, which is broken down to heme as the globin parts are turned into amino acids. The heme is then turned into unconjugated bilirubin in the reticuloendothelial cells of the spleen. This unconjugated bilirubin is not soluble in water, due to intramolecular hydrogen bonding. It is then bound to albumin and sent to the liver.
The measurement of direct bilirubin depends on its reaction with diazosulfanilic acid to create azobilirubin. However, unconjugated bilirubin also reacts slowly with diazosulfanilic acid, so that the measured indirect bilirubin is an underestimate of the true unconjugated concentration.
In the liver it is conjugated with glucuronic acid by the enzyme glucuronyltransferase, making it soluble in water. Much of it goes into the bile and thus out into the small intestine. However 95% of the secreted bile is reabsorbed by the small intestine. This bile is then resecreted by the liver into the small intestine. This process is known as enterohepatic circulation. About half of the conjugated bilirubin remaining in the large intestine(about 5% of what was originally secreted) is metabolised by colonic bacteria to form urobilinogen, which maybe further oxidized to urobilin and stercobilin. Urobilin, stercobilin and their degradation products give feces its brown color.However, just like bile, some of the urobilinogen is reabsorbed and 95% of what is reabsorbed is resecreted in the bile which is also part of enterohepatic circulation. A small amount of the reabsorbed urobilinogen (about 5%) is excreted in the urine following further oxidation to urobilin which gives urine its characteristic yellow color. This whole process results in only 1–20% of secreted bile being lost in the feces. The amount lost depends on the secretion rate of bile. Although the terms direct and indirect bilirubin are used equivalently with conjugated and unconjugated bilirubin, this is not quantitatively correct, because the direct fraction includes both conjugated bilirubin and δ bilirubin (bilirubin covalently bound to albumin, which appears in serum when hepatic excretion of conjugated bilirubin is impaired in patients with hepatobiliary disease).Furthermore, direct bilirubin tends to overestimate conjugated bilirubin levels due to unconjugated bilirubin that has reacted with diazosulfanilic acid, leading to increased azobilirubin levels (and increased direct bilirubin).
Under normal circumstances, a tiny amount of urobilinogen, if any, is excreted in the urine. If the liver's function is impaired or when biliary drainage is blocked, some of the conjugated bilirubin leaks out of the hepatocytes and appears in the urine, turning it dark amber. However, in disorders involving hemolytic anemia, an increased number of red blood cells are broken down, causing an increase in the amount of unconjugated bilirubin in the blood. Because the unconjugated bilirubin is not water-soluble, one will not see an increase in bilirubin in the urine. Because there is no problem with the liver or bile systems, this excess unconjugated bilirubin will go through all of the normal processing mechanisms that occur (e.g., conjugation, excretion in bile, metabolism to urobilinogen, reabsorption) and will show up as an increase in urine urobilinogen. This difference between increased urine bilirubin and increased urine urobilinogen helps to distinguish between various disorders in those systems.
Bilirubin is a yellowish pigment found in bile, a fluid made by the liver.A small amount of older red blood cells are replaced by new blood cells every day. Bilirubin is left after these older blood cells are removed. The liver helps break down bilirubin so that it can be removed by the body in the stool.
Bilirubin testing checks for levels of bilirubin in your blood. Bilirubin (bil-ih-ROO-bin), an orange-yellow pigment, is a waste product of the normal breakdown of red blood cells. Bilirubin passes through the liver and eventually out of the body — mostly in feces, a small amount in urine.
Before reaching the liver, bilirubin is called unconjugated, meaning uncombined. In the liver, bilirubin combines with certain sugars to create a water-soluble form called conjugated bilirubin. Conjugated bilirubin passes out of the liver, and in the colon, it is converted back into the unconjugated form en route to being excreted from the body.
Most laboratories use a test that detects conjugated bilirubin, which is called direct. By subtracting the direct bilirubin from the amount of total bilirubin, an estimate of unconjugated bilirubin, called indirect, is obtained.
Higher than normal levels of direct or indirect bilirubin may indicate different types of liver problems. Occasionally, higher bilirubin levels may indicate an increased rate of destruction of red blood cells (hemolysis).
Bilirubin (3D-balls Structure)
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 brown color.
Bilirubin circulates in the bloodstream in two forms:
Indirect (or unconjugated) bilirubin. This form of bilirubin does not 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) and is made by the liver from indirect bilirubin.
Total bilirubin and direct bilirubin levels are measured directly in the blood, whereas 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 appear 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.
Too much bilirubin (hyperbilirubinemia) in a newborn baby can cause brain damage (kernicterus), hearing loss, problems with the muscles that move the eye, physical abnormalities, and even death. Therefore, some babies who develop jaundice may be treated with special lights (phototherapy ) or a blood transfusion to lower their bilirubin levels.
In a newborn baby, the blood sample is usually taken from the heel (heel stick).
Hepatocellular causes of elevation include hepatitis, cirrhosis, and advanced neoplastic states. Increased with cholestatic drug reactions, Dubin-Johnson syndrome, and Rotor syndrome. In the latter two syndromes, the level is usually <5 mg/dL.
Theoretically, direct bilirubin should not be increased in hemolytic anemias, in which bilirubin increase should be in the indirect bilirubin fraction in the absence of complications. In practice, some increase in the direct fraction may be encountered in patients with hemolytic anemia in whom complications have not been proven. Some methods have shown the direct bilirubin to be spuriously high. This may be due to different concentrations of sodium nitrite, which may convert some of the unconjugated bilirubin to conjugated bilirubin.Direct bilirubin is the water soluble fraction. When increased in serum, bilirubin should become positive in the urine. Physiologic jaundice, occurring two to four days after birth, is due to lack of liver glucuronyl transferase.
Bilirubin, Direct testing may be used to screen for liver disease or when someone may have been exposed to hepatitis viruses. The Bilirubin, Direct test helps evaluate liver and biliary disease. Increased direct bilirubin occurs with biliary diseases, including both intrahepatic and extrahepatic lesions. Hepatocellular causes of elevation include hepatitis, cirrhosis, and advanced neoplastic states. Turnaround time for the Bilirubin test is typically 1 business day.
Why do I need this test and how should I get ready for the test?
Bilirubin is an orange-yellow pigment, a waste product primarily produced by the normal breakdown of heme, a substance found mainly in the protein hemoglobin in red blood cells (RBCs). It is ultimately processed by the liver to allow its elimination from the body. This test measures the amount of bilirubin in the blood in order to evaluate liver function or to help diagnose anemia caused by the increased destruction of RBCs (hemolytic anemia).
RBCs normally degrade after about 120 days in the circulation. As the heme in hemoglobin is broken down, it is converted into bilirubin; this form is also called unconjugated bilirubin. Unconjugated bilirubin is not very soluble in water, so it is carried by proteins to the liver, where sugars are attached (conjugated) to it to form water-soluble conjugated bilirubin. This conjugated bilirubin enters the bile and passes from the liver to the small intestines, where it is further broken down by bacteria and eventually eliminated in the stool. The breakdown products of bilirubin give stool its characteristic brown color.
Approximately 250 to 350 mg of bilirubin is produced daily in a normal, healthy adult, of which 85% is derived from damaged or degraded red cells, with the remaining amount 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 (a sum of these) may also be reported. The pattern of results from these tests can give the doctor information as to the condition that may be present.
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. Elevated unconjugated bilirubin may mean that too much is being produced, usually due to increased destruction (hemolysis) of RBCs, or that the liver is incapable of processing bilirubin due to liver diseases such as cirrhosis or inherited problems. Elevated conjugated bilirubin may indicate that the liver can process bilirubin but it is not adequately removed in a timely manner due to acute hepatitis or blockage of bile ducts.
It is not uncommon to see high total and unconjugated bilirubin levels in newborns, typically 1 to 3 days old. This is sometimes called physiologic jaundice of the newborn and is due to immaturity of the newborn's liver. This situation usually resolves itself within a few days. In hemolytic disease of the newborn, RBCs may be destroyed because of blood incompatibilities between the baby and the mother, and treatment may be needed because high levels of unconjugated bilirubin can cause damage to 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 and must be quickly detected and treated, usually with surgery, to prevent serious liver damage (cirrhosis) that may require liver transplantation within the first year or two of life. Even after surgery, some children still may require liver transplantation.
Bilirubin testing is usually done as part of a group of tests to evaluate the health of your liver. Bilirubin testing may be done to:
- Investigate jaundice — elevated levels of bilirubin can cause yellowing of your skin and the whites of your eyes (jaundice). The most common use of the test is to measure bilirubin levels in newborns.
- Determine whether there's a blockage in your liver's bile ducts
- Help detect or monitor the progression of other liver disease, such as hepatitis
- Help detect increased destruction of red blood cells
- Help follow how a treatment is working
- Help evaluate suspected drug toxicity
Some common tests that might be done at the same time as bilirubin testing include:
- Liver function tests. A group of blood tests that measure certain enzymes or proteins in your blood.
- Albumin and total protein. Levels of albumin — a protein made by the liver — and total protein show how well your liver is making proteins that your body needs to fight infections and perform other functions.
- Complete blood count. This test measures several components and features of your blood.
- Prothrombin time. This test measures the clotting time of plasma.
In adults and older children, bilirubin is measured to diagnose and/or monitor liver diseases, such as cirrhosis, hepatitis, or gallstones. It is also used to evaluate people with sickle cell disease or other causes of hemolytic anemia who may have episodes when excessive red blood cell destruction takes place, increasing bilirubin levels. Bilirubin can be measured as a total level and/or as conjugated and unconjugated levels for these purposes. More commonly, the laboratory uses a chemical test to detect water-soluble forms of bilirubin, termed direct bilirubin, which is an estimate of the amount of conjugated bilirubin. By subtracting this from the total bilirubin, an indirect estimate (indirect bilirubin) of unconjugated bilirubin is obtained.
In newborns with jaundice, bilirubin is measured to investigate the cause. Excessive unconjugated bilirubin damages developing brain cells in infants and may cause mental retardation, learning and developmental disabilities, hearing loss, or eye movement problems. It is important that an elevated level of bilirubin in a newborn be identified and quickly treated. In both physiologic jaundice of the newborn and hemolytic disease of the newborn, only unconjugated (indirect) bilirubin is increased. In the much less common cases of damage to the liver (neonatal hepatitis and biliary atresia), conjugated (direct) bilirubin elevations are present as well, often providing the first evidence that one of these less common conditions is present.
A doctor 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 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
Determining a bilirubin level in newborns with jaundice is considered standard medical care.
The test 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.
Thus, 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.
Originally the Van den Bergh reaction was used for a qualitative estimate of bilirubin.
Van den Bergh reaction is a chemical reaction used to measure bilirubin levels in blood. More specifically, it determines the amount of conjugated bilirubin in the blood. The reaction produces azobilirubin. Principle:bilirubin reacts with diazotised sulphanilic acid to produce purple coloured azo bilirubin.
This test is performed routinely in most medical laboratories and can be measured by a variety of methods.
Total bilirubin is now often measured by the 2,5-dichlorophenyldiazonium (DPD) method, and direct bilirubin is often measured by the method of Jendrassik and Grof.
Blood sample from a heel stick
For a heel stick blood sample, several drops of blood are collected from the heel of your baby. 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, and 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 your baby's bilirubin level is high.
Blood sample from a vein
The health professional taking a sample of your blood will:
- Wrap an elastic band around your upper arm to stop the flow of blood. This makes the veins below the band larger so it is easier to put a needle into the vein.
- Clean the needle site with alcohol.
- Put the needle into the vein. More than one needle stick may be needed.
- Attach a tube to the needle to fill it with blood.
- Remove the band from your arm when enough blood is collected.
- Put a gauze pad or cotton ball over the needle site as the needle is removed.
- Put pressure on the site and then put on a bandage.
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. Your baby may feel a little discomfort with the skin puncture.
Blood sample from a vein
The blood sample is taken from a vein in your arm. An elastic band is wrapped around your upper arm. It may feel tight. You may feel nothing at all from the needle, or you may feel a quick sting or pinch.
There is very little chance of a problem from a heel stick. A small bruise may develop at the site.
There is very little chance of a problem from having a blood sample taken from a vein.
- You may get a small bruise at the site. You can lower the chance of bruising by keeping pressure on the site for several minutes.
- In rare cases, the vein may become swollen after the blood sample is taken. This problem is called phlebitis. A warm compress can be used several times a day to treat this.
- Ongoing bleeding can be a problem for people with bleeding disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can make bleeding more likely. If you have bleeding or clotting problems, or if you take blood-thinning medicine, tell your doctor before your blood sample is taken.
Bilirubin testing is done using a blood sample. Usually, the blood is drawn through a small needle inserted into a vein in the bend of your arm. You'll be asked to roll up your shirt sleeve if you're wearing long sleeves. The person drawing the blood might tie a band around your upper arm and ask you to make a fist. This causes your vein to stand out more, making it easier to insert the needle into the vein. The needle is attached to a small tube, in which your blood is collected. All of this usually takes just a few minutes.
Blood for bilirubin testing in newborns is usually obtained using a sharp lance to break the skin of the heel (heel stick).
You may feel a quick pain as the needle is inserted into your arm and experience some short-term discomfort at the site after the needle is removed.
After the test
Once the needle is removed, a piece of gauze and a bandage or similar material will be placed over the area where the needle was inserted. You'll be asked to gently apply pressure to the area for a minute or so, to help stop any bleeding.
Your blood will be sent to a laboratory for analysis. If the laboratory analysis is done on-site, you could have your test results within hours. If your doctor sends your blood to an off-site laboratory, you may receive the results within several days.
How to prepare?
Adults should not eat or drink for 4 hours before a bilirubin test. No special preparation is needed for children before having a bilirubin test.
Tell your doctor if you:
- Are taking any medicines.
- Are allergic to any medicines.
- Have had bleeding problems or take blood-thinners, such as aspirin or warfarin (Coumadin).
- Are or might be pregnant.
Talk to your doctor about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will mean. To help you understand the importance of this test, fill out the medical test information form.
What are normal results for this test?
Normal results for a typical bilirubin test are 0.1 to 1 milligram per deciliter (mg/dL) of total bilirubin (direct plus indirect) and 0 to 0.3 mg/dL for direct. These results may vary slightly from laboratory to laboratory and are typical for adult men. Normal results may be slightly different for women and children, and results may be affected by certain foods, medications or strenuous exercise. Be sure to tell your doctor about any foods or medications you've taken and your activity levels so that your results can be interpreted correctly.
Lower than normal bilirubin levels are usually not a concern. Elevated levels may indicate liver damage or disease.
Higher than normal levels of direct bilirubin in your blood may indicate your liver isn't clearing bilirubin properly, for example, because of a blocked bile duct. Elevated levels of indirect bilirubin may indicate other problems. One common, and harmless, cause of elevated bilirubin is Gilbert's syndrome, a deficiency in an enzyme that helps break down bilirubin. Your doctor may order further tests to investigate your condition. Bilirubin test results also may be used to monitor the progression of certain conditions such as jaundice.
It is normal to have some bilirubin in your blood. Normal levels are:
- Direct (also called conjugated) bilirubin: 0 to 0.3 mg/dL
- Total bilirubin: 0.3 to 1.9 mg/dL
Note: mg/dL = milligrams per deciliter
Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.
The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.
Adults and children
Increased total bilirubin that is mainly unconjugated (indirect) bilirubin may be a result of:
- Hemolytic or pernicious anemia
- Transfusion reaction
- A common metabolic condition termed Gilbert syndrome, due to low levels of the enzyme that attaches sugar molecules to 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 some kind of blockage of the bile ducts. This may occur, for example, with:
- Gallstones getting into the bile ducts
- Scarring of the bile ducts
Rare inherited disorders that cause abnormal bilirubin metabolism (Rotor, Dubin-Johnson, Crigler-Najjar syndromes) may also cause increased levels of bilirubin.
Low levels of bilirubin are not generally a concern 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 rapidly increases, an investigation of the cause is needed so appropriate treatment can be initiated. An elevated bilirubin level may result from the accelerated breakdown of red blood cells due to a blood type incompatibility between the mother and her newborn. Other causes include certain congenital infections, hypoxia, a number of different genetic disorders, and 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.
Although unconjugated bilirubin may be toxic to brain development in newborns (up to the age of about 2–4 weeks), high bilirubin in older children and adults does not pose the same threat. In older children and adults, the "blood-brain barrier" is more developed and prevents bilirubin from crossing this barrier to the brain cells. Elevated bilirubin levels in children or adults, however, strongly suggest a medical condition that must be evaluated and treated.
Bilirubin is not normally present in the urine. However, conjugated bilirubin is water-soluble and therefore may be eliminated from the body in the urine when levels increase in the body. Its presence in the urine usually indicates blockage of liver or bile ducts, hepatitis or some other liver damage. The most common method for detecting urine bilirubin is the dipstick test that is part of a urinalysis.
Bilirubin levels tend to be slightly higher in males than females, while African Americans show lower values. Strenuous exercise may also increase bilirubin levels.
The drug atazanavir increases levels of unconjugated (indirect) bilirubin. Drugs that can decrease levels of total bilirubin include barbiturates, caffeine, penicillin, and high doses of salicylates.
A bilirubin test measures the amount of bilirubin in a blood sample. The results are usually available in 1 to 2 hours.
Normal values in adults
The normal values listed here-called a reference range-are just a guide. These ranges vary from lab to lab, and your lab may have a different range for what?s normal. Your lab report should contain the range your lab uses. Also, your doctor will evaluate your results based on your health and other factors. This means that a value that falls outside the normal values listed here may still be normal for you or your lab.
Bilirubin levels in adults
0.0-0.2 mg/dL or 0.0-3.4 mmol/L
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.
Total bilirubin levels in newborns up to 7 days old
Less than 24 hours
Less than 6.0 mg/dL or less than 103 mmol/L
Less than 48 hours
Less than 12.0 mg/dL or less than 205 mmol/L
Less than 10.0 mg/dL or less than 170 mmol/L
3 to 5 days
Less than 15.0 mg/dL or less than 256 mmol/L
Less than 12.0 mg/dL or less than 205 mmol/L
Less than 15.0 mg/dL or less than 256 mmol/L
Less than 10.0 mg/dL or less than 170 mmol/L
What might affect my test results?
High levels of bilirubin in the blood may be caused by:
- Some infections, such as an infected gallbladder, or cholecystitis.
- Some inherited diseases, such as Gilbert's syndrome, a condition that affects how the liver processes bilirubin. Although jaundice may occur in some people with Gilbert's syndrome, the condition is not harmful.
- 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, indomethacin (Indocin), phenytoin (Dilantin), diazepam (Valium), and flurazepam (Dalmane).
Low levels of bilirubin in the blood may be caused by: Medicines that may decrease bilirubin levels. This includes vitamin C, phenobarbital, and theophylline.
Are some people more at genetic risk of abnormal bilirubin levels?
Several inherited chronic conditions include Gilbert syndrome, Dubin-Johnson syndrome, Rotor syndrome, and Crigler-Najjar syndrome. Of these four syndromes, Crigler-Najjar is the most serious and may result in death. The first three are usually mild, chronic conditions that can be aggravated under certain conditions but in general cause no significant health problems. Gilbert syndrome is very common; about 1 in every 6 people have the genetic abnormality, although most do not have elevated bilirubin levels.
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 in severe cases, and certain drugs may 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 often is resolved by surgery to remove the blockage. 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.
Reasons you may not be able to have the test or why the results may not be helpful (except in newborns) include:
- Caffeine, which can lower bilirubin levels.
- Not eating for a long period (fasting), which normally increases indirect bilirubin levels.
What To Think About
- A common cause of jaundice in newborns is a condition called physiologic jaundice. It occurs in healthy babies when they are 1 to 3 days old for several reasons, including the increased breakdown of red blood cells right after birth. It usually disappears on its own within a week without causing problems. But in some cases, a baby with physiologic jaundice may need treatment with special lights (phototherapy) to prevent serious problems.
- A premature baby's liver is immature and may not be able to break down bilirubin properly in the blood. This is one of the reasons premature babies are more likely than full-term babies to develop jaundice.
- Bilirubin can be measured in amniotic fluid if your doctor thinks that your unborn baby may have a condition that destroys red blood cells (erythroblastosis fetalis). For more information, see the topic Amniocentesis.
- Bilirubin may also be measured in the urine. Normally, urine does not contain any bilirubin. If bilirubin is detected in urine, additional testing may be needed to determine the cause. High amounts of bilirubin in urine may indicate that the bilirubin is not being removed from the body by the liver.
- Using a transcutaneous bilirubin test, doctors can screen all newborns for jaundice. They place a device gently against the skin to check bilirubin levels before a baby goes home from the hospital.