bilirubin (redirected from Bilirubin metabolism)

bilirubin /bil·i·ru·bin/ (-roo´bin) a bile pigment produced by 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 bile. High concentrations of bilirubin may result in jaundice.

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conjugated bilirubin , direct bilirubin bilirubin that has been taken up by the liver cells and conjugated to form the water-soluble bilirubin diglucuronide.

indirect bilirubin , unconjugated bilirubin the lipid-soluble form of bilirubin that circulates in loose association with the plasma proteins.

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bil·i·ru·bin (bl-rbn, bl-r-)

n.

A red bile pigment derived from the degradation of hemoglobin during the normal and abnormal destruction of red blood cells.

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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

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bilirubin

[bil′iro̅o̅′bin]

Etymology: L, bilis + ruber, red

the orange-yellow pigment of bile, formed principally by the breakdown of hemoglobin in red blood cells after termination of their normal lifespan. Water-insoluble unconjugated bilirubin normally travels in the bloodstream to the liver, where it is converted to a water-soluble, conjugated form and excreted into the bile. In a healthy person, about 250 mg of bilirubin is produced daily. The majority of bilirubin is excreted in the stool. The characteristic yellow pallor of jaundice is caused by the accumulation of bilirubin in the blood and in the tissues of the skin. Testing for bilirubin in the blood provides information for diagnosis and evaluation of liver disease, biliary obstruction, and hemolytic anemia. Normal levels of total bilirubin are 0.1 to 1 mg/dl or 5.1 to 17 μmol/L. See also jaundice, van den Bergh's test.

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bilirubin [bil″ĭ-roo´bin]

a yellow to orange 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 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.

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bilirubin

an orange 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. 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 thus lead to obstructive or regurgitation jaundice.

Another type of jaundice results from excessive destruction of erythrocytes (hemolytic or retention jaundice). The more rapid the destruction of red blood cells and the degradation of hemoglobin, the greater the amount of bilirubin in the body fluids.

Most bilirubin is excreted in the feces. A small amount is excreted in the urine as urobilinogen.

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conjugated bilirubin

bilirubin that has been conjugated, mainly to glucuronic acid, in the liver and gives a direct result to the van den bergh test. High blood levels indicate obstructive or hepatocellular origin of the jaundice.

delta bilirubin

see biliprotein.

bilirubin diglucuronide

see conjugated bilirubin (above).

free bilirubin

see unconjugated bilirubin (below).

bilirubin toxicity

see kernicterus.

unconjugated bilirubin

bilirubin that has not been conjugated in the liver. It gives an indirect reaction to the van den bergh test. A high level of it in the blood is indicative of hemolysis or a lack of bilirubin clearance by the liver. Called also free bilirubin.

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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.