Jaundice is the yellow discolouration of the skin, sclerae and mucous membranes caused by raised levels of bilirubin in the blood. It is a clinical sign rather than a diagnosis in its own right, and it becomes visible only once the serum bilirubin rises well above the normal range, typically around double the upper limit or higher.
Bilirubin is produced when haemoglobin from ageing red blood cells is broken down. In its unconjugated form it is not water soluble and travels bound to albumin. The liver conjugates it, making it water soluble, and it is then excreted in bile into the gut. Jaundice occurs when any step in that pathway is overwhelmed or obstructed.
The pattern of accompanying symptoms narrows the cause considerably. Pale stools and dark urine point towards obstruction. Itching is common in cholestasis. Painless jaundice with weight loss raises concern about pancreatic malignancy, whereas colicky right upper quadrant pain suggests stones. Investigation typically combines liver function tests, a coagulation screen, viral serology and ultrasound, with further imaging or endoscopic procedures as indicated.
Jaundice in newborns is common and often physiological, reflecting immature liver enzymes and a high red cell turnover. It still needs assessment, because very high unconjugated bilirubin can cross the blood brain barrier and cause kernicterus, a permanent neurological injury. Management is guided by bilirubin level plotted against age in hours on treatment threshold charts, using phototherapy and, rarely, exchange transfusion. Jaundice appearing within the first 24 hours, or persisting beyond two weeks, always requires investigation.
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