All people have a certain amount of bilirubin in their blood. Its norm should be no more than 17.1 μmol / l. Sometimes situations arise when bilirubin in the body is produced in more quantity than a healthy liver can produce under normal functioning. Bilirubin may also increase due to liver damage, which can interfere with the excretion of bilirubin. In addition, when blocking the bile duct of the liver, bilirubin is excreted very slowly and in small quantities. The norm of its content in the blood is exceeded. This condition is called hyperbilirubinemia. In this case, bilirubin in the body accumulates to a certain concentration, after which it penetrates into the tissues, giving them a yellow color. This condition is called jaundice.
In order to more fully and correctly understand why jaundice may appear, you should first understand how bilirubin is exchanged in general. Bilirubin appears from heme, which in the body is mainly contained in the form of hemoproteins. Hemoglobin released during the breakdown of mature red blood cells is the most significant source of bilirubin (70-80%). The rest of the bilirubin is formed in approximately equal parts from the hemoglobin of immature red blood cells and their precursors in the bone marrow and from heme-containing enzymes such as catalase, cytochrome, etc. At the same time, 250-400 mg is the total amount in which an adult forms every day. human bilirubin. The norm for passing the analysis is 0.2-1.0 mg / dl.
If the bilirubin contained in the plasma begins to exceed the allowable threshold, then jaundice develops. This happens because bilirubin, the norm of which is significantly exceeded, begins to bind to the elastic fibers of the conjunctiva and skin. According to the mechanism of its formation, jaundice is of three types:
- Hemolytic (or suprahepatic).
- Caused by parenchymal damage to the liver (hepatocellular).
- Caused by obstruction of the biliary tract (subhepatic or mechanical).
Hemolytic jaundice is characterized by abundant formation of unconjugated bilirubin or its stagnation in the body. In plasma, total bilirubin rises due to unconjugated. In urine, bilirubin is completely absent. This is explained by the inability of unconjugated bilirubin to penetrate through the renal filter, which is not damaged. Hemolytic jaundice can be caused by hemolytic crisis, malaria, intravascular hemolysis, toxins, vitamin B12 deficiency, and transfusion of incompatible blood. The level of unconjugated bilirubin can be increased with Gilbert's syndrome. People with this syndrome almost all the time notice yellowness of the mucous membranes and skin. The reason for this is that the liver is unable to capture, conjugate and excrete bilirubin into the bile capillaries.
With parenchymal jaundice, both conjugated and unconjugated bilirubin increase simultaneously . Most often, the cause of this situation may be impaired clearance of unconjugated bilirubin from the blood, impaired secretion of conjugated bilirubin from the liver cells into the bile capillaries, as well as the passage of conjugated bilirubin from bile-filled capillaries of the bile into the blood vessels through damaged liver cells. In this case, an increased level of bilirubin in the blood serum is accompanied by an increase in its excretion in the urine. However, at the first stages of the development of the disease in the urine, bilirubin is almost not determined, therefore such a test cannot be called an early diagnosis.
Mechanical jaundice is caused by hepatic obstruction of the biliary tract, impaired outflow of bile or complete closure of the bile duct (tumor, inflammation, stone, etc.). With this type of jaundice, the hepatic capillaries are stretched, because bile accumulates in the liver, hepatocytes begin to squeeze and pass conjugated bilirubin into the blood capillaries . Its norm in blood plasma rises, and even if the permissible renal threshold (about 30 µmol / L) is exceeded, then bilirubin appears in the urine.