Why this test?
To find out if the increase in total bilirubin is due to a blockage of the bile ducts (due to stones, narrowing of the bile ducts or a tumor) or liver disease such as hepatitis or cirrhosis.
In what cases is it prescribed?
A test for direct bilirubin is prescribed when the level of total bilirubin increases. In addition, it can be part of standard diagnostic panels used in routine medical examinations and in preparation for surgical intervention. It is also usually included in a panel of so-called liver tests, which are used to assess liver function.
In addition, this study is prescribed for obvious signs of jaundice, if there is evidence of long-term alcohol abuse, and if the patient complains of weakness, fatigue, loss of appetite, nausea, vomiting, abdominal pain (especially in the right hypochondrium), darkening of urine or lightening of the stool, itching of the skin.
Bilirubin is an orange-yellow pigment found in bile and gives it its characteristic color. Normally, erythrocytes circulate in the blood for about 120 days, and then they are destroyed. During their destruction, the hemoglobin included in their composition (a red pigment that carries oxygen from the lungs to the tissues) turns into indirect (unlinked, unconjugated) bilirubin. About 250-350 mg of bilirubin is normally formed every day, of which 85% comes from destroyed erythrocytes, and the rest - from the bone marrow and liver.
Indirect bilirubin enters the liver, where a sugar-containing substance is added to it, making it soluble in water. Such bilirubin is called direct (linked, conjugated). Direct bilirubin from the liver cells moves into the bile ducts and is transported with bile to the intestines. Under the influence of normal intestinal microflora, the sugar-containing substance is split off from bilirubin, and it itself turns into a brown pigment, which gives the characteristic color of feces, which is then excreted from the body.
Normally, direct bilirubin is almost not contained in the blood. Its concentration increases in cases when the liver is able to metabolize bilirubin, but cannot remove it in time. Most often, this happens due to blockage of the bile ducts (then mainly only direct bilirubin will increase), as well as due to damage to the liver structure in hepatitis and cirrhosis (then both direct and indirect bilirubin will increase).
When the outflow of bile is obstructed, bilirubin does not enter the intestine and, accordingly, does not turn into a brown pigment, which is why the feces lighten. Excess amounts of direct bilirubin, entering the urine, begin to give it a dark color.