When carrying out a biochemical blood test, three bilirubin indices are distinguished: direct fraction, indirect fraction, total bilirubin (the sum of the direct and indirect fractions). The formation of direct and indirect bilirubin proceeds according to different mechanisms, therefore, in order to correctly establish the diagnosis in the biochemical analysis of venous blood, it is necessary to distinguish which bilirubin is increased - direct or indirect. Consider what is direct (bound, conjugated) bilirubin, what are the normal values of this indicator, and what does it mean if the direct bilirubin in the blood is elevated.
The formation of direct bilirubin in the body
This fraction of the bilirubin pigment is a chemical compound that is formed in hepatocytes (liver cells), after which most of it gets together with bile in the intestine. There, it is split and excreted from the body, mainly with feces and in smaller amounts - through the kidneys. A small part of the direct bilirubin comes from the liver cells into the bloodstream.
Direct bilirubin is less toxic (compared to indirect bilirubin), this fraction is well water soluble. The name "direct" bilirubin comes from the fact that this substance gives a direct reaction with a diazo reagent (an aqueous solution of diazophenylsulphonic acid) used in biochemical analysis.
The norm and diagnostic value of direct bilirubin
The indicator of direct bilirubin of blood is a sensitive marker of liver pathologies. Its norm for adults is in the range from 0.86 to 5.3 μmol / l, which is about a quarter of the value of total bilirubin in the blood. It is worth noting that the exact upper limit of the norm depends on the reagents that are used to determine this index, but the error does not exceed 10-15%.
By itself, direct bilirubin does not pose a special threat to human health, tk. he is connected, and, consequently, is rendered harmless and must leave the bloodstream. But it is important that there are no barriers in its path, and the connection intended for withdrawal is not returned back.
Increased concentration of direct bilirubin fraction (conjugation hyperbilirubinemia) signals pathological processes. In this case, direct bilirubin accumulates in the elastic tissues of the body, eyeballs, skin. Clinically in patients, this can be expressed by symptoms such as darkening of the urine, pain in the right hypochondrium, skin itching, jaundice.
What does elevated direct bilirubin mean?
If the direct bilirubin in the blood is increased, the reasons for this may be related to various pathological mechanisms, namely:
- with increased hemolysis (destruction) of blood cells of erythrocytes, causing excess bilirubin;
- with violation of metabolic transformations of bilirubin in hepatocytes;
- with a mechanical violation of excretion of bilirubin from the body.
Diseases that can be called the causes of an increased content of direct bilirubin in the blood include:
- infectious liver damage (including viral and bacterial hepatitis);
- toxic and drug-induced hepatitis;
- autoimmune hepatitis (including those associated with autoimmune lesions of other organs);
- intrahepatic cholestasis;
- biliary cirrhosis ;
- pancreatic tumors;
- cholelithiasis;
- helminthic lesions;
- liver tumors (including cancer);
- metastases to the liver;
- Dabin-Johnson syndrome;
- Rotor syndrome;
- sclerosing cholangitis;
- jaundice of pregnant women, etc.