Bilirubin
Bilirubin is a brownish-yellow substance found in bile, which is produced by the liver and stored in the gallbladder. This liquid plays a crucial role in digesting fats by being released into the small intestine. Bilirubin is generated through the breakdown of old or damaged red blood cells and exists in two forms: indirect (unconjugated) bilirubin, which is not water-soluble, and direct (conjugated) bilirubin, which is water-soluble and can be eliminated by the body. Elevated levels of bilirubin, known as hyperbilirubinemia, can lead to jaundice, characterized by a yellow tint in the skin and eyes. This condition is particularly common in newborns, whose immature livers may struggle to process bilirubin efficiently. Various medical issues, including liver diseases and gallbladder disorders, can lead to increased bilirubin levels, while certain medications may also affect these levels. Doctors often conduct blood tests to measure bilirubin concentrations, aiding in the diagnosis of underlying health problems.
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Bilirubin
Bilirubin is a substance found in bile. Bile is a thick liquid containing acids that helps the body digest fats. The liver produces bile, which is stored in the gallbladder. Bile is released into the small intestine to help digest food. Bilirubin is brownish yellow.
An overabundance of bilirubin can cause a number of health issues and can help doctors detect other medical problems, such as liver disorders. Medical experts may request blood tests to determine the amount of bilirubin and diagnose health issues such as liver problems or some types of cancer.
Overview
Bilirubin circulates throughout the body in blood. This is known as indirect, or unconjugated, bilirubin. Old or damaged red blood cells collect in the liver, which breaks them down and creates bile. The liver processes the indirect bilirubin and makes direct, or conjugated, bilirubin. In this form, the bilirubin is attached to sugar and is soluble, meaning it can dissolve in water. Converting it to a soluble form allows the body to eliminate the excess bilirubin.
The bile containing direct bilirubin is dispensed into the digestive system through bile ducts. In the digestive tract, bacteria transform it to mesobilirubinogen and urobilinogen. Some of the urobilinogen is reabsorbed into the blood, while the rest leaves the body through defecation, and is responsible for the color of normal stools.
Sometimes the body has too much bilirubin, a condition called hyperbilirubinemia. This can cause jaundice, which is when bilirubin collects in the tissue of the body. The most recognizable sign of jaundice is a yellow tint to the skin and eyes.
Newborns sometimes have too much bilirubin because the red blood cells are breaking down at a high rate and their livers are not yet efficiently removing bilirubin from the blood. Too much bilirubin in infants can cause serious problems, including brain damage or kernicterus. Usually newborns who experience jaundice within the first few days after birth are not affected, and it disappears quickly. If the condition does not go away on its own, infants must be treated to reduce bilirubin levels. Infants with too much bilirubin may need light treatment or, in rare severe cases, blood transfusions.
A number of medical conditions may cause high levels of bilirubin. These include gallbladder disorders, infections, inherited conditions that affect the liver, hepatitis and other diseases that damage the liver, gallstones and other causes of bile duct blockage, and maladies that destroy red blood cells. Some medications, including some antibiotics and birth control pills, also can raise bilirubin levels. Low levels of bilirubin may be due to medications such as phenobarbital and theophylline.
Some bacterial infections can change the conjugated bilirubin back to unconjugated bilirubin and acid. This can allow calcium from the bilirubin to form stones. These stones can block the bile duct, causing jaundice and pain.
Doctors may order blood tests to measure indirect, direct, or combined total bilirubin levels.
Bibliography
"Bile – Higher Tier." GCSE Bitesize/BBC, www.bbc.co.uk/schools/gcsebitesize/science/add‗edexcel/common‗systems/digestionrev4.shtml. Accessed 3 Oct. 2016.
Case-Lo, Christine. "Bilirubin Blood Test." Healthline, 5 July 2016, www.healthline.com/health/bilirubin-blood. Accessed 3 Oct. 2016.
"Facts about Jaundice and Kernicterus." Centers for Disease Control and Prevention, 23 Feb. 2015, www.cdc.gov/ncbddd/jaundice/facts.html. Accessed 3 Oct. 2016.
Healthwise Staff. "Bilirubin." WebMD, 21 Aug. 2015, www.webmd.com/digestive-disorders/bilirubin-15434#1. Accessed 3 Oct. 2016.
Lightner, David A. Bilirubin: Jekyll and Hyde Pigment of Life. Springer, 2013.
"Liver Function Tests." WebMD, www.webmd.com/a-to-z-guides/liver-function-test-lft#1. Accessed 3 Oct. 2016.
Rodak, Bernadette F., George A. Fritsma, and Kathryn Doig, editors. Hematology: Clinical Principles and Applications. Saunders Elsevier, 2007.
Weisiger, Richard A. "Conjugated Hyperbilirubinemia." Medscape, 5 Jan. 2016, emedicine.medscape.com/article/178757-overview. Accessed 3 Oct. 2016.