Bilirubin is produced when the liver breaks down old red blood cells. The levels of bilirubin in the body are normally low, so elevated levels may indicate certain diseases such as those that impair liver function, bock bile ducts, or cause increased destruction of red blood cells.
Bilirubin is a yellow-brown substance found in bile. It is a waste product that leaves the body through urine and stool, giving stool its normal brown color and urine its yellow color. It also gives bruises their yellow color.
The bilirubin level found in the body reflects the balance between production and excretion. Increased bilirubin levels may be due to liver disease (such as hepatitis), blood disorders (such as hemolytic anemia), or blockage of the bile ducts through which bile flows from the liver to the small intestine. An allergic reaction to the blood received during a transfusion can also cause the levels of bilirubin to rise in adults.
A bilirubin test measures the amount of bilirubin found in a small sample of blood. Because bilirubin exists in the blood in two forms, two measurements are taken:
(1) Indirect (or unconjugated) bilirubin: This form is not water-soluble; it ends up in the liver, where it is changed into a soluble form (direct or conjugated).
(2) Direct (or conjugated) bilirubin: This form is water-soluble and is made by the liver from indirect bilirubin.
Three values are normally provided: Total bilirubin, direct bilirubin, and indirect bilirubin. The first two are measured directly in the blood sample; the indirect bilirubin level is calculated from the first two. Results are usually available in 1 to 2 hours.
Certain medicines can damage the liver. Examples include many antibiotics, some types of birth control pill (sex hormones), antipsychotic drugs, and many others.
One common – and harmless – cause of elevated bilirubin is Gilbert's syndrome, a deficiency in an enzyme that helps break down bilirubin.
Diseases that cause liver damage can lead to increased bilirubin levels. To further investigate the cause of jaundice or increased bilirubin levels, liver function tests or other evidence of infective hepatitis (hepatitis A, B, C, delta, E, etc.) are commonly used.
Certain conditions, such as hemolytic anemia, can cause increased destruction of red blood cells and therefore increased bilirubin production.
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