Bilirubin

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Bilirubin

The predominant orange pigment of bile. It is the major metabolic breakdown product of heme, the prosthetic group of hemoglobin in red blood cells, and other chromoproteins such as myoglobin, cytochrome, and catalase. The breakdown of hemoglobin from the old red cells takes place at a rapid rate in the reticuloendothelial cells of the liver, spleen, and bone marrow. The steps in this breakdown process include denaturation and removal of the protein globin, oxidation and opening of the tetrapyrrole ring, and the removal of iron to form the green pigment biliverdin, which is then reduced to bilirubin by the addition of hydrogen. The formed bilirubin is transported to the liver, probably bound to albumin, where it is conjugated into water-soluble mono- and diglucuronides and to a lesser extent with sulfate. See Liver

In mammalian bile essentially all of the bilirubin is present as a glucuronide conjugate. Bilirubin glucuronide is passed through the liver cells into the bile caniculi and then into the intestine. The bacterial flora further reduces the bilirubin to colorless urobilinogen. Most of the urobilinogen is either reduced to stercobilinogen or oxidized to urobilin. These two compounds are then converted to stercobilin, which is excreted in the feces and gives the stool its brown color. See Hemoglobin

Bilirubin

 

C33H36O6N4, a bile pigment; molecular mass 584.68. Brown crystals. Bilirubin is an intermediate product of the decomposition of hemoglobin that takes place in the macrophages of the spleen, liver, and bone marrow. It is formed by the enzymatic reduction of biliverdin. It is present in small quantities in the plasma of vertebrate animals and man (0.2–1.4 mg percent in a healthy person). When the outflow of bile is made difficult (obstruction of the bile ducts), and in some liver diseases, the bilirubin concentration increases in the blood (causing jaundice), and it appears in the urine. Hence, the presence of bilirubin in blood or urine is a diagnostic test.

bilirubin

[‚bil·ə′rü·bən]
(biochemistry)
C33H36N4O6 An orange, crystalline pigment occurring in bile; the major metabolic breakdown product of heme.
References in periodicals archive ?
The models were refit controlling for baseline factors: age, gender, dark urine, AST, ALT, indirect bilirubin, direct bilirubin, scleral icterus, and type of hepatitis (acute, chronic, undiagnosed source).
Blood chemistry concentrations included total and indirect bilirubin 5.
Any patient presenting with jaundice should have a complete blood count and peripheral smear evaluation, especially if the indirect bilirubin is high, to exclude hemolysis.
For elevated total bilirubin levels, obtain direct and indirect bilirubin levels.
The following variables were considered: plasma cholesterol concentration, albumin, total protein, fibrinogen, creatinine, urate, alkaline phosphatase, [gamma]-glutamyltranspeptidase, total and indirect bilirubin, prothrombin activity, hematocrit, hemoglobin, blood cell counts, number of resected liver segments, duration of the operation and of eventual liver ischemia, occurrence of cirrhosis, neoplastic disease, previous chemotherapy, associated bowel operations, sepsis, cholestasis, and substrate doses in patients on parenteral nutrition.
In each subject, after an overnight fast, plasma concentrations of total and direct-reacting bilirubin were determined by a diazo method at least three times within 6 months before the study; indirect bilirubin was calculated as total minus direct bilirubin.