Bilirubin

enUK

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.

Bilirubin

enUK

bilirubin

[bil″ĭ-roo´bin] a yellow to orange pigment" >bile pigment produced by the breakdown of heme and reduction of biliverdin; it normally circulates in plasma and is taken up by liver cells and conjugated to form bilirubin diglucuronide, the water-soluble pigment excreted in the bile.

Bilirubin. The metabolism of bilirubin. Once bile is taken up and conjugated by the liver, some leakage of bilirubin mono- and diglucuronides does occur, but these normally account for less than 5% of circulating bilirubin. In bile, more than 80% is conjugated as the diglucuronide form. From Aspinall and Taylor-Robinson, 2001. Failure of the liver cells to excrete bile, or obstruction of the bile ducts, can cause an increased amount of bilirubin in the body fluids and lead to jaundice" >obstructive jaundice.
Another type of jaundice, hemolytic jaundice, results from excessive destruction of erythrocytes. The more rapid the erythrocyte destruction and hemoglobin degradation, the greater the amount of bilirubin in body fluids.
Laboratory tests for the determination of bilirubin content in the blood are of value in diagnosing liver dysfunction and in evaluating hemolytic anemias. (See accompanying table.) Bilirubin may be classified as indirect (“free” or unconjugated) while en route to the liver from its site of formation by reticuloendothelial cells, and direct (bilirubin diglucuronide) after its conjugation in the liver with glucuronic acid. Elevated indirect bilirubin levels indicate prehepatic jaundice, such as hemolytic jaundice, or certain types of hepatic jaundice involving inability to conjugate bilirubin. Elevated direct bilirubin levels indicate other types of hepatic jaundice, such as in viral or alcoholic hepatitis, or posthepatic jaundice, as in biliary obstruction.
Normally the body produces a total of about 260 mg of bilirubin per day. Almost 99 per cent of this is excreted in the feces; the remaining 1 per cent is excreted in the urine as urobilinogen.

bil·i·ru·bin

(bil'i-rū'bin), A yellow bile pigment found as sodium bilirubinate (soluble), or as an insoluble calcium salt in gallstones; formed from hemoglobin during normal and abnormal destruction of erythrocytes by the reticuloendothelial system; a bilin with substituents on the 2, 3, 7, 8, 12, 13, 17, and 18 carbon atoms and with oxygens on carbons 1 and 19. Excess bilirubin is associated with jaundice. [bili- + L. ruber, red]

bilirubin

(bĭl′ĭ-ro͞o′bĭn, bĭl′ĭ-ro͞o′-)n. A reddish-yellow bile pigment, C₃₃H₃₆N₄O₆, derived from the degradation of heme.

bilirubin

A yellow-red haemoglobin-breakdown product derived from catabolised RBCs, present in bile transported from the liver to the gallbladder to the intestines. BR gives bile its colour and is normally passed in stool; increased production or decreased excretion of BR results in cutaneous and ocular sclera jaundice. BR that has not been metabolised in the liver is termed indirect bilirubin (BRI) and is attached to albumin in the circulation; after hepatic metabolism, it is no longer bound to proteins, and is called direct bilirubin (BRD). The sum of BRD and BRI equals total bilirubin (BRT), which is usually measured as part of a routine chemistry profile and in liver profiles; if BRT is increased, the lab automatically measures BRD; BRI is a calculated value of BRT – BRD.

Ref range
BRT, umbilical cord <2.0 mg/dL; 0–1 day of life <6.0 mg/dL; 1–2 days <8.0 mg/dL; 3–5 days <12 mg/dL; thereafter <0.2–1.0 mg/dL; BRD BRI is increased in liver damage, hemolytic anaemia, congenital enzyme deficiencies; BRD is increased in biliary obstruction; RT is increased in continuous hemolysis and biliary obstruction with hepatic damage.

Urine
Negative.

Amniotic fluid
28 weeks <0.075 mg/dL; 40 weeks <0.025 mg/dL.

bilirubin

BR Lab medicine A yellow-red Hb breakdown product derived from catabolized RBCs, present in bile transported from the liver to the gallbladder to the intestines; BR gives bile its color and is normally passed in stool; ↑ production or ↓ excretion of BR results in jaundice of the skin and ocular sclera; BR that has not been metabolized in the liver is indirect bilirubin–BR_I, and is attached to albumin in the circulation; after hepatic metabolism, it is no longer bound to proteins, and is called direct bilirubin–BR_D; the sum of BR_D and BR_I is total bilirubin–BR_T, which is usually measured as part of a routine chemistry profile, and in liver profiles; if BR_T is ↑, the laboratory automatically measures BR_D; BR_I is a calculated value of BR_T – BR_D Ref range BR_T, umbilical cord <2.0 mg/dL; 0-1 day of life <6.0 mg/dL; 1-2 day <8.0 mg/dL; 3-5 day <12 mg/dL, thereafter <0.2-1.0 mg/dL; BR_D < 0.3 mg/dL; BR_I 0.2–1.3 mg/dL; BR_T 0.3–1.6 mg/dL; BR_I is ↑ in liver damage, hemolytic anemia, congenital enzyme deficiencies; BR_D is ↑ in biliary obstruction; BR_T is ↑ in continuous hemolysis, biliary obstruction with hepatic damage Urine Negative Amniotic fluid 28 wk <0.075 mg/dL; 40 wk <0.025 mg/dL See Conjugated bilirubin, Delta bilirubin.

bil·i·ru·bin

(bil'i-rū'bin) A yellow bile pigment found as sodium bilirubinate (soluble),or as an insoluble calcium salt in gallstones, formed from hemoglobin during normal and abnormal destruction of erythrocytes by the reticuloendothelial system. Excess levels of bilirubin are associated with jaundice. [bili- + L. ruber, red]

bilirubin

A coloured substance in bile derived from the breakdown of haemoglobin in effete red blood cells at the end of their 120 day life. Bilirubin is conjugated with glucuronic acid in the liver and excreted in the bile, giving the stools their characteristic colour. When it cannot escape freely into the bowel it accumulates in the blood, staining the skin to cause JAUNDICE. The stools become pale and the urine dark. Conjugated bilirubin is water-soluble.

bilirubin

a reddish-yellow BILE pigment.

Bilirubin

A pigment produced by the liver that is excreted in bile which causes a yellow discoloration of the skin and eyes when it accumulates in those organs. Bilirubin levels can be measured by blood tests, and are most often elevated in patients with liver disease or a blockage to bile flow.Mentioned in: Cholangitis, Cholecystitis, Erythroblastosis Fetalis, Gallbladder x Rays, Gallstones, Glucose-6-Phosphate Dehydrogenase Deficiency, Jaundice, Liver Disease, Neonatal Jaundice, Sickle Cell Disease, Thalassemia

bilirubin

bil·i·ru·bin

bilirubin

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Bilirubin

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bil·i·ru·bin

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Synonyms for bilirubin

noun an orange-yellow pigment in the bile that forms as a product of hemoglobin

Synonyms

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