Bilirubin is a product of red blood cells that are metabolized in the body. It can be divided into total bilirubin, indirect bilirubin, and direct bilirubin.
The lifespan of normal red blood cells is 120 days, and a large number of senescent red blood cells die and destroy every day, and are broken down and metabolized in the spleen and bone marrow mononucleus-macrophage system to become heme and heme. Under the action of ions, biliverdin is generated, and biliverdin produces bilirubin.
Bilirubin is indirect bilirubin after entering the liver with the bloodstream and is not converted to direct bilirubin. After entering the liver, glucuronosyl bilirubin is formed under the action of glucuronidase converting enzyme, that is, direct bilirubin. Most of the direct bilirubin is excreted into the intestine with bile and reduced to urinary (fecal) biliform, which is excreted in the stool. A small part is absorbed back into the liver and then discharged into the intestine through the biliary tract, forming a hepatoenteric circulation. In addition, a small amount of urobilinogen is excreted through the kidneys through the systemic circulation.
The sum of indirect bilirubin and direct bilirubin in the blood is total bilirubin.
Indirect bilirubin elevation: due to the inability of hepatic function to synthesize direct bilirubin, hepatocyte jaundice, or prehepatic hemolytic jaundice.
Elevated direct bilirubin: obstructive jaundice occurs due to the inability of direct bilirubin synthesized in the liver to be excreted into the biliary tract. It is seen in liver duct stones, bile duct stones, acute jaundice hepatitis, chronic jaundice hepatitis, liver cirrhosis, liver cancer blood group incompatibility during blood transfusion, etc.
Elevated total bilirubin: seen in a variety of disorders with indirect and direct bilirubin elevations.
Laboratory examination of bilirubin is an indispensable item for liver function examination and biliary tract disease examination, which is of great significance for the diagnosis and differential diagnosis of jaundice. In some cases, there may be a transient mild increase in bilirubin, which is more common after drinking alcohol and exercising, which is a physiological phenomenon and should not be bothered.