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Bilirubin Metabolism And its Role in Neonatal Jaundice

BY: Zandro Cabaral | Category: Bioinformatics | Submitted: 2011-01-18 10:40:07
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Article Summary: "This article describes the metabolism of bilirubin and how the defect in its metabolism causes jaundice in neonates..."

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Bilirubin comes from dead Red Blood Cells which when lysed, immit Heme and Globin. Heme is then acted upon by the enzyme Heme oxygenase to form Biliverdin. Another enzyme known as biliverdin reductase acts on Biliverdin to form the end product. Albumin then bounds to hemoglobin and forms bilirubin-albumin complex. The complex is acted upon the enzyme Glucoronyl transferase to form conjugated bilirubin. Enzyme beta glucoronidase acts on the conjugated bilirubin and excretes it in the urine in the form of Urobilinogen. However, in abnormal cases, bilirubin conjugation is arrested or absent which results in the deposition of unconjugated bilirubin.

A deposition of excess bilirubin in the body is known as Hyperbilirubinemia. It is common in neonates and is manifested by Neonatal jaundice. An excess in unconjugated bilirubin in the serum of the neonate causes a yellowish discoloration in the skin, a greenish or brown stool and may collect in the basal ganglia of the brain and cause Kernicterus.

Neonatal jaundice can be Physiologic and Pathologic jaundice. Physiologic jaundice appears on the second to the third day of life and disappears on the fifth day. It peaks on the second to third day with peak bilirubin levels of ten to twelve (10-12) milligrams per deciliter at a rate of less than five (5) milligrams per deciliter per day. On the other hand, Pathologic jaundice appears in the first twenty-four hours of life with unlimited peak bilirubin levels at a rate of more than five (5) milligrams per deciliter per day. Of these two etiologies, the pathologic jaundice gives a greater treat to neonates.

Neonatal jaundice maybe caused by the following:
• Increased bilirubin production or load on the liver such as hemolytic diseases like Spherocytosis, ABO and Rh alloimmunization and Hemoglobinopathies.
• Increase in extrahepatic circulation in cases such as Pyloric stenosis, Breastmilk jaundice and bowel obstruction.
• Metabolic abnormalities such as Criggler-Najjar Syndrome and Gilbert Syndrome.
• Cephalhematomas wherein there are occult hemorrhages in the brain.
• Infants of diabetic mothers.
• Decrease clearance in cases of premature babies.

The most fatal effect of hyperbilirubinemia of the neonates is Kernicterus or bilirubin encephalopathy which is the accumulation of excess bilirubin in the brain. Kernicterus has four phases. Phase ONE presents with poor sucking, hypotonia and depressed sensorium. Phase TWO presents with fever and hypotonia. Phase THREE is characterized by a high pitched cry, poor feeding, athetosis, hearing and visual abnormalities. If the hyperbilirubinemia is left untreated, the disease progresses into a long term disease and presents with the baby having an upward gaze palsy sensorineural hearing loss and mental retardation.

The treatment of Unconjugated hyperbilirubinemia is by Phototherapy which is the geometric photoisomerization of unconjugated bilirubin. The "Blue Light" is the most recommended by Physicians due to its faster effect and less harmful effects to the neonates like burns and optical damage. Photooxidation and structural isomerization can also be used. The pharmacologic therapies for neonatal jaundice are the Phenobarbital which causes induction of glucoronyl transferase activity and enhances hepatic uptake. Another drug used are the Metalloporphyrins which inhibit heme oxygenase. Another method used to correct neonatal hyperbilirubinemia is the Blood Exchage Transfusion which is the process wherein extracting neonate's blood and transfusing new blood of the same type. Eighty-five percent of circulating red blood cells are replaced when the equivalent of two neonatal blood volumes are used.

There is also a type of neonatal jaundice which is associated with breastfeeding. This is usually noted in the first week of life which causes decrease milk intake and results to dehydration. Decrease in the intake of milk by the neonate also results in the decrease in the caloric intake which may result to hypoglycemia and malnutrition. Treatment of this type is the discontinuation of breastfeeding and introduction of formulated milk.

Another type of neonatal jaundice is Cholestatic jaundice. In this type, there is a prolonged elevation of conjugated bilirubin and maybe a result of intrahepatic diseases such as neonatal sepsis and metabolic disorders and extrahepatic diseases such as Biliary atresia. The diagnostics and work-up of this type of hyperbilirubinemia includes history and physical examination, metabolic screening, serologic studies, ultrasonography, hepatobiliary scintigraphy and liver biopsy. Management of this type includes phototherapy with a close monitoring of serum bilirubin levels until normal.

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