Pathophysiology of the neonatal Jaundice

Abstract

This article presents a brief review of billirubin metabolism. According to recent investigations on billirubin chemistry and metabolism three-dimensional billirubin molecule has no fixed shape. It is a flexible molecule than can assume a large number of shapes of different stability. Due to the presence of hydrogen-bonds between juxtaposed NH/O and OH/O groupings of billirubin molecule, the hydrophilic polar-COOH and-NH groups are intimately associated and unavailable for interaction with polar groups in the environment. Consequently, billirubin is essentially insoluble in water but is lipophilic, hence unconjugated billirubin passes readily across biologic membranes such as placenta, blood-brain barrier and hepatocyte membrane being inherently difficult to excrete. Billirubin is conjugated mainly with glucoronic acid in the liver. Since glucoronic acid contains several polar-OH and -COOH groups, conjugated billirubin is more water soluble and less lipophilic than the unconjugated billirubin and polar enough to be excreted in bile and is nontoxic to CNS. The pathogenesis of billirubin encephalopathy is complex and poorly understood. In general, there is a increased risk of developing kernicterus when there is either an increased in risk of developing kernicterus when there is either an increase in "Free" billirubin in the circulation or when binding capacity approaches close to albumin saturation. Although various techniques are available to measure free billirubin and albumin binding capacity, the classical use of total and unconjugated billirubin in levels in conjunction with clinical judgment remains a valuable alternative.