A yellow hue of the skin caused by abnormally high levels of bilirubin in the body. As red blood cells are replaced in the body, the waste products from this replacement are normally eliminated by the liver. Bilirubin is one of those waste products. Before birth, the placenta is very efficient in removing bilirubin from the baby's blood; the baby's liver does not need to remove the bilirubin. After delivery the infant's liver must take over this elimination function. It takes a few weeks for the baby's liver to fully achieve this function. Until the liver can keep up with the formation of bilirubin, there is a build-up of bilirubin in the body. Bilirubin is yellow, and when the levels are high, it appears in the skin and other tissues, as a yellowish color.
At low to moderate levels the main effect of bilirubin is to make the skin appear yellow. However, when the levels of bilirubin get high, the bilirubin can enter the cells of the brain and damage them. Concern about brain injury prompts frequent measurement of the bilirubin level in newborns. It is much easier to treat the bilirubin level when it is only moderately high rather than when it is dangerously high.
At low levels of bilirubin accumulation, increasing an infant's fluid intake and using phototherapy (light therapy) may be all that is required to reduce the bilirubin level or keep it at a safe level. At high levels of bilirubin, an exchange transfusion that essentially exchanges the baby's own bilirubin-laden blood with low-bilirubin-containing blood from an adult donor may be necessary to reduce the risk of brain injury. It is the need to keep the bilirubin level from getting too high and the complex nature of the exchange transfusion for high bilirubin levels that prompts doctors to measure and be concerned about the bilirubin level. Many hospitals are currently adopting the practice of checking the level of bilirubin, of every newborn, either with an external meter or by checking the blood directly, for earlier detection of this problem.