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Bilirubin
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LP15448-1 Bilirubin
Bilirubin is an orange-yellow pigment produced by the normal breakdown of heme, a component of the hemoglobin found in red blood cells. It is processed by the liver and excreted in bile. Conditions that cause red blood cell breakdown or interfere with liver or bile processing can cause elevated levels of bilirubin. Bilirubin exists in many forms. Non-glucuronidated bilirubin (also called unconjugated or indirect) is the breakdown product of heme and is not water-soluble. Hemolytic anemias, which cause increased red blood cell breakdown, are one cause of elevated non-glucuronidated bilirubin. Glucuronidated bilirubin (also called conjugated) is a water-soluble form of bilirubin that is made in the liver by the addition of sugar molecules to non-glucuronidated bilirubin. Conditions that affect liver function (such as hepatitis, cirrhosis and liver tumors) or physically block the bile ducts (such as gallstones) can cause elevated levels of glucuronidated bilirubin. A third form of bilirubin is that which is bound to albumin, and it is also known as delta bilirubin because it was originally identified based on the unexpected difference between the total bilirubin level and the level of glucuronidated plus non-glucuronidated bilirubin in some patient samples. Prior to the discovery of albumin-bound bilirubin, the term "direct" bilirubin was used as a synonym for glucuronidated bilirubin, but direct bilirubin is actually glucuronidated plus delta bilirubin (bilirubin covalently bound to albumin).
Source: Regenstrief LOINC
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