Jaundice in the newborn

[Luis Fok]

Jaundice is a yellow color to the skin and/or eyes caused by an increase in bilirubin in the bloodstream. Bilirubin is a yellow substance formed when hemoglobin (the part of red blood cells that carries oxygen) is broken down as part of the normal process of recycling old or damaged red blood cells. Bilirubin is carried in the bloodstream to the liver and processed so that it can be excreted out of the liver as part of bile (the digestive fluid produced by the liver). Bilirubin processing in the liver involves attaching it to another chemical substance in a process called conjugation.

Processed bilirubin in the bile is thus called conjugated bilirubin.
Unprocessed bilirubin is called unconjugated bilirubin.

Bile is transported through the bile ducts into the beginning of the small intestine (duodenum). If bilirubin cannot be processed and excreted by the liver and bile ducts quickly enough, it builds up in the blood (hyperbilirubinemia). As bilirubin levels in the blood increase, the whites of the eyes turn yellow first, followed by the skin. During the first week of life, the majority of full-term newborns develop unconjugated hyperbilirubinemia, often causing jaundice that normally resolves within a week or two (physiologic jaundice). Jaundice caused by unconjugated hyperbilirubinemia is even more common among premature infants.
Bile is transported through the bile ducts into the beginning of the small intestine (duodenum). If bilirubin cannot be processed and excreted by the liver and bile ducts quickly enough, it builds up in the blood (hyperbilirubinemia). The excess bilirubin settles in the skin, the whites of the eyes, and other tissues, causing them to turn yellow (jaundice).
(See also Jaundice in Adults.)