Jaundice

Abstract

Jaundice is a common clinical sign characterized most recognizably by yellow staining of the conjunctiva, mucous membranes, and skin due to an elevated bilirubin level in the blood. The majority of bilirubin (about 4 mg per kg produced daily) derives from the breakdown of red blood cells and their constituent hemoglobin. The remainder results from ineffective erythropoiesis and the degradation of muscle and cytochromes. In health, circulating unconjugated bilirubin is taken up by hepatocytes, where it becomes conjugated with glucuronic acid. Conjugated bilirubin is then excreted from the liver through bile, stool, and urine. Jaundice may represent predominately excess unconjugated bilirubin (“indirect bilirubin”) or an excess of unconjugated and conjugated (“direct”) bilirubin. Clinical measurement of serum bilirubin includes “fractionation” of the total concentration into these two moieties and provides the first and critical clue to diagnosis.