Bilirubin (fractions)

1. Bilirubin is a bile pigment that is formed as a result of the breakdown of hemoglobin and other heme-containing proteins, which are mainly found in destroyed erythrocytes. In the process of metabolism, bilirubin goes through several stages: first, indirect (unconjugated, free) bilirubin is formed, which is toxic and is transported to the liver. In the liver, it binds to glucuronic acid, turning into direct (conjugated, bound) bilirubin - a water-soluble form that is safely excreted in bile through the biliary tract into the intestine.

Determination of bilirubin fractions (total, direct and indirect) is a key tool in gastroenterology and hepatology. A comprehensive analysis allows you to accurately determine the cause of jaundice (yellowing of the skin and sclera) or increased enzyme levels: whether it is associated with liver cell damage, problems with bile duct patency (mechanical jaundice), or with massive destruction of erythrocytes (hemolytic anemia).

Key indicators (what determines the test)

• Total bilirubin: The total concentration of both fractions (direct and indirect) of bilirubin in the blood serum (μmol/L).

• Direct (conjugated) bilirubin: The fraction cleared by the liver. Its elevation usually indicates a disorder of bile outflow (cholestasis, cholelithiasis, ductal tumors).

• Indirect (free) bilirubin: A toxic fraction that is insoluble in water. Its elevation is characteristic of intense destruction of red blood cells (hemolysis) or congenital enzyme disorders (e.g. Gilbert's syndrome).

Preparation for the study To ensure maximum accuracy of blood test results, the following rules should be followed:

• Fasting: Blood is donated in the morning on an empty stomach (it is recommended to fast for 8–12 hours; drinking clean, non-carbonated water is allowed).

• Nutrition: The night before, you should avoid fatty, fried, and spicy foods, as well as alcohol.

• Physical and emotional state: One day before the study, avoid intense physical activity, stress, and sudden changes in regimen.

• Medications: Consult your doctor in advance about the medications you are taking, as some drugs may affect pigment metabolism.

• Bad habits: Refrain from smoking at least 1–2 hours before donating blood.

Frequently Asked Questions (FAQ)

• Why is it important to determine the bilirubin fractions, and not just the total? Total bilirubin shows only the general picture, while the ratio of its fractions (direct and indirect) helps the doctor accurately determine the source of the problem: is it a pathology of the liver itself, a violation of the outflow of bile, or problems with the blood (hemolysis).

• What is Gilbert's syndrome and why is it related to bilirubin? It is an inherited metabolic disorder in which there is a moderate increase in indirect bilirubin in the blood (usually against the background of stress, starvation or overwork), while other liver parameters remain normal, and it is not a dangerous disease.

• When does a doctor order this test? The test is ordered if jaundice (skin or sclera of the eyes) appears, pain in the right hypochondrium, dark urine or discoloration of feces, suspected hepatitis, as well as during routine preventive examinations or monitoring of hepatotoxic medications.