Bilirubin is a yellowish pigment produced during the breakdown of red blood cells. It circulates in the bloodstream and is eventually processed by the liver, where it is conjugated (chemically modified) to make it water-soluble and easier to excrete from the body.
Direct bilirubin, also known as conjugated bilirubin, refers to bilirubin that has undergone conjugation in the liver. Conjugated bilirubin is water-soluble and can be excreted into bile, which then flows into the digestive tract and is ultimately eliminated from the body in the feces. Elevations in direct bilirubin levels can occur due to various liver and biliary tract disorders, including:
Biliary obstruction: Blockage of the bile ducts by gallstones, tumors, or inflammation (e.g., due to pancreatitis) can impair the flow of bile and lead to elevated direct bilirubin levels.
Liver diseases: Conditions that affect liver function, such as hepatitis, cirrhosis, and liver cancer, can result in impaired bilirubin conjugation and excretion, leading to elevated direct bilirubin levels.
Intrahepatic cholestasis: Liver conditions that disrupt bile formation or secretion within the liver can cause an increase in direct bilirubin levels. Examples include primary biliary cholangitis and intrahepatic cholestasis of pregnancy.
Gilbert syndrome: This is a genetic condition characterized by mild, intermittent elevations in bilirubin levels, including both indirect and direct bilirubin. It is typically benign and does not require treatment.
Measurement of direct bilirubin levels, along with total bilirubin and indirect bilirubin levels, is commonly performed as part of liver function tests. Elevated direct bilirubin levels, particularly when accompanied by other abnormal liver function test results, may indicate liver or biliary tract dysfunction and often warrant further evaluation to determine the underlying cause.
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