Bilirubin is a yellow compound that occurs in the normal catabolic pathway that breaks down heme in vertebrates. This catabolism is a necessary process in the body's clearance of waste products that arise from the destruction of aged or abnormal red blood cells. For example, the molecules excreted in the urine differ from those in the feces. Bilirubin is excreted in bile and urineand elevated levels may indicate certain diseases. Its subsequent breakdown products, such as stercobilincause the brown color of faeces.
A different breakdown product, urobilinis the main component of the straw-yellow color in urine. It has also been found in plants. Bilirubin consists of an open chain tetrapyrrole. It is formed by oxidative cleavage of a porphyrin in heme, which affords biliverdin. Biliverdin is reduced to bilirubin.
After conjugatation with glucuronic acidbilirubin is excreted. Bilirubin is il bilirubin è lalcolismo alzato similar to the pigment phycobilin used by certain algae to capture light energy, and to the pigment phytochrome used by plants to sense light. All of these contain an open chain of four pyrrolic rings. Like these other pigments, some of the double-bonds in bilirubin isomerize when exposed to light.
This isomerization is relevant to the phototherapy of jaundiced newborns: the E,Z-isomers of bilirubin formed upon light exposure are more soluble than the unilluminated Z,Z-isomer, as the possibility of intramolecular hydrogen bonding is removed.
Some textbooks and research articles show the incorrect geometric isomer of bilirubin. Bilirubin is created by the activity of biliverdin reductase on biliverdina green tetrapyrrolic bile pigment that is also a product of heme catabolism. Bilirubin, when oxidized, reverts to become biliverdin once again. This cycle, in addition to the demonstration of the potent antioxidant activity of bilirubin,  has led to the hypothesis that bilirubin's main physiologic role is as a cellular antioxidant.
The measurement of il bilirubin è lalcolismo alzato bilirubin is underestimated by measurement of indirect bilirubin, as unconjugated bilirubin without glucuronidation reacts with diazosulfanilic acid to create azobilirubin which is measured as direct bilirubin. In the liver, bilirubin is conjugated with glucuronic acid by the enzyme glucuronyltransferasemaking it soluble in water: the conjugated version is the main form of bilirubin present in the "direct" bilirubin fraction.
Much of it goes into the bile and thus out into the small intestine. Though most bile acid is reabsorbed in the terminal ileum to participate in enterohepatic circulationconjugated bilirubin is not absorbed and instead passes into the colon. There, colonic bacteria deconjugate and metabolize the bilirubin into colorless urobilinogenwhich can be oxidized to form urobilin and stercobilin.
Urobilin is excreted by the kidneys to give urine its yellow color and stercobilin is excreted in the faeces giving stool its characteristic brown color. Under normal circumstances, only a very small amount, if any, of urobilinogen, is excreted il bilirubin è lalcolismo alzato the urine. If the liver's function is impaired or when biliary drainage is blocked, some of the conjugated bilirubin leaks out of the hepatocytes and appears in the urine, turning it dark amber.
However, in disorders involving hemolytic anemiaan increased number of red blood cells are broken down, causing an increase in the amount of unconjugated bilirubin in the blood. Because the unconjugated bilirubin is not water soluble, one will not see an increase il bilirubin è lalcolismo alzato bilirubin in the urine. Because there is no problem with the liver or bile systems, this excess unconjugated bilirubin will go through all of the normal processing mechanisms that occur e.
This difference between increased urine bilirubin and increased urine urobilinogen helps to distinguish between various disorders in those systems. Unconjugated hyperbilirubinaemia in a newborn can lead to accumulation of bilirubin in certain brain regions particularly the basal nuclei with consequent irreversible damage to these areas manifesting as various neurological deficits, seizuresabnormal reflexes and il bilirubin è lalcolismo alzato movements.
This type of neurological injury is known as kernicterus. The spectrum of clinical effect is called bilirubin encephalopathy. The neurotoxicity of neonatal hyperbilirubinemia manifests because the blood—brain barrier has yet to develop fully, [ dubious il bilirubin è lalcolismo alzato discuss ] and bilirubin can freely pass into the brain interstitium, whereas more developed individuals with increased bilirubin in the blood are protected.
Aside from specific chronic medical conditions that may lead to hyperbilirubinaemianeonates in general are at increased risk since they lack the intestinal bacteria that facilitate the breakdown and excretion of conjugated bilirubin in the faeces this is largely why the faeces of a neonate are paler than those of an adult.
In the absence of liver disease, high levels of total bilirubin confers various health benefits. Bilirubin is degraded by light. Blood collection tubes containing blood or especially serum to be used in bilirubin assays should be protected from illumination. For adults, blood is typically collected by needle from a vein in the arm.
In il bilirubin è lalcolismo alzato, blood is often collected from a heel stick, a technique that uses a small, sharp blade to cut the skin on the infant's heel and collect a few drops of blood into a small tube. Non-invasive technology is available in some health care facilities that will measure bilirubin by using an instrument placed on the skin transcutaneous bilirubin meter. Note: Conjugated bilirubin is often incorrectly called "direct bilirubin" and unconjugated bilirubin is incorrectly called "indirect bilirubin".
Direct and indirect refer solely to how compounds are measured or detected in solution. Likewise, not all conjugated bilirubin is readily available in solution for reaction or detection for example, if it is hydrogen bonding with itself il bilirubin è lalcolismo alzato therefore would not be included in the direct bilirubin fraction.
Total bilirubin assays work by using surfactants and accelerators like caffeine to bring all of the different bilirubin forms into solution where they can react with assay reagents. Total and direct bilirubin levels can be measured from the blood, but indirect bilirubin is calculated from the total and direct bilirubin.
Indirect bilirubin is fat-soluble and direct bilirubin is water-soluble. Originally, the Van den Bergh reaction was used for a qualitative estimate of bilirubin.
This test is performed routinely in most medical laboratories and can be measured by a variety of methods. Total bilirubin is now often measured by the 2,5-dichlorophenyldiazonium DPD method, and direct bilirubin is il bilirubin è lalcolismo alzato measured by the method of Jendrassik and Grof. The bilirubin level found in the body reflects the balance between production and excretion. Blood test results should always be interpreted using the reference range provided by the laboratory that performed the test.
Typical ranges for adults are: . Hyperbilirubinemia is a higher-than-normal level of bilirubin in the blood. Moderate [ clarification needed ] rise in bilirubin may be caused by:. Very high [ clarification needed ] levels of bilirubin may be caused by:. Cirrhosis may cause normal, moderately high or high levels of bilirubin, depending on exact features of the cirrhosis. To further elucidate the causes of jaundice or increased bilirubin, il bilirubin è lalcolismo alzato is usually simpler to look at other liver function tests especially the enzymes alanine transaminaseaspartate transaminasegamma-glutamyl transpeptidasealkaline phosphataseblood film examination hemolysisetc.
Jaundice is classified, depending upon whether the bilirubin is free or conjugated to glucuronic acid, into conjugated jaundice or unconjugated jaundice. Urine bilirubin may also be clinically significant. If the blood level of conjugated bilirubin becomes elevated, e.
Testing urine for both bilirubin and urobilinogen can help differentiate obstructive liver disease from other causes of jaundice. Bilirubin was discovered by Rudolf Virchow in From Wikipedia, the free encyclopedia. Redirected from Billy Rubin. Interactive image Interactive image. PubChem CID. Chemical formula. Structure and properties. Spectral data. Main article: Kernicterus. EVAN 3 May Merck Manuals Professional Edition in Latin. Retrieved 5 May National Library of Medicine.
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