Total bilirubin Laboratory research

General Information

Bilirubin Is one of the major components of bile. It is produced by enzymatic catabolism of the heme fraction in macrophages from various hemoproteins.

About 80% of circulating bilirubin is derived from aged erythrocytes. When circulating erythrocytes reach the end of their normal life, after about 120 days, they are destroyed by reticuloendothelial cells, during which oxidation of the secreted heme produces biliverdin, which in turn is metabolized to bilirubin.

The remaining 15-20% of circulating bilirubin is produced from other sources: as a result of the destruction of mature erythrocytes in the bone marrow or other proteins containing heme - liver cytochromes, muscle myoglobin, metabolism of enzymes.

The bilirubin (unconjugated) thus circulated in the blood and transferred to the liver as a soluble bilirubin-albumin complex. In the liver it conjugates to glucuronic acid by exposure to UDP-glucuronyl transferases. Conjugated bilirubin includes bilirubin-monoglucuronide, which predominates in the liver, and bilirubin-diglucuronide, which predominates in bile. Conjugated bilirubin is transported to the bile ducts, from where it is excreted with bile, passes into the intestine, and is converted to urobilinogen and stercobilinogen. A small amount of stercobilinogen and urobilinogen is excreted in the feces;

Serum bilirubin levels increase when bilirubin production exceeds its metabolism and excretion. Clinically, hyperbilirubinemia manifests itself in the form of jaundice - yellow pigmentation of the skin and sclera.