An elevated bilirubin level in the blood that is caused by an abnormal metabolism of bilirubin by the liver. Bilirubin is a breakdown product of red blood cells. The disorder is inherited and one in five Caucasians has a mild form of the condition. The disorder causes an elevated blood level of a kind of bilirubin (unconjugated bilirubin). On occasion, the bilirubin is elevated enough that there is a slight yellow coloring of the skin. Gilbert's disease is otherwise not dangerous and very few other symptoms are experienced.