Bilirubin: Description
A yellow bile pigment found as sodium bilirubinate (soluble), or as an insoluble calcium salt in gallstones; formed from hemoglobin during normal and abnormal destruction of erythrocytes by the reticuloendothelial system; a bilin with substituents on the 2, 3, 7, 8, 12, 13, 17, and 18 carbon atoms and with oxygens on carbons 1 and 19. Excess pigment is associated with jaundice.
Terminology related with this pigment include
- Conjugated.
- Indirect reacting.
- Unconjugated.
- Delta.
- Direct reactin.
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 of it into the bile.
This pigment 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, the pigment 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 pigment. Because the pigment is chemically different after it goes through the conjugation process in the liver, lab tests can differentiate between the unconjugated or indirect the pigment and conjugated or direct bilirubin. The terms “direct” and “indirect” reflect the way the two types of the pigment 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. Total bilirubin measures both BU and BC.
Increased indirect or total of this pigment may be a sign of:
- Hepatitis.
- Crigler-Najjar syndrome.
- Erythroblastosis fetalis.
- Gilbert’s disease.
- Sickle cell anemia.
- Transfusion reaction.
- Pernicious anemia.
- Bruise or bleeding under the skin.
- Hemolytic anemia.
- Hemolytic disease of the newborn.
This pigment 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 pigment is usually increased in relation to the severity of the acute process.
Increased direct this pigment may indicate:
- Intrahepatic cholestasis.
- Bile duct obstruction.
- Cirrhosis.
- Dubin-Johnson syndrome.
Drugs that can increase bilirubin measurements include, anabolic steroids, allopurinol some antibiotics, , azathioprine, antimalaria medications, chlorpropamide, cholinergics, codeine, diuretics, epinephrine, meperidine, methyldopa, methotrexate, MAO inhibitors, morphine, nicotinic acid, birth control pills, phenothiazines, quinidine, rifampin, steroids, sulfonamides, and theophylline.
Drugs that can decrease the pigment measurements include caffeine, barbiturates, penicillin, and high-dose salicylates such as aspirin.
The 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.
Talk to your health professional about any concerns you have regarding the need for the test, its risks, how it will be done, or what the results will indicate. To help you understand the importance of this test.
DISCLAIMER: This information should not substitute for seeking responsible, professional medical care.