During a routine pre employment physical examination, an apparently healthy 24 year old man is found to have increased serum levels of unconjugated bilirubin. Conjugated bilirubin and transaminases are normal. Careful questioning reveals no evidence of recent illnesses. Which of the following is the most likely diagnosis?

Gilbe's syndrome is a relatively common hereditary condition that is so mild, a case can be made for classifying it as a normal variant rather than a true disease. It produces asymptomatic unconjugated hyperbilirubinemia, and is impoant to know about to avoid unnecessary diagnostic procedures. Crigler-Najjar syndrome (choice A) represents several hereditary diseases characterized by severe unconjugated hyperbilirubinemia. The type I form, in paicular, can be fatal. Dubin-Johnson and Rotor syndromes are relatively mild hereditary conjugated hyperbilirubinemias. Ref: Murray R.K. (2011). Chapter 31. Porphyrins & Bile Pigments. In D.A. Bender, K.M. Botham, P.A. Weil, P.J. Kennelly, R.K. Murray, V.W. Rodwell (Eds), Harper's Illustrated Biochemistry, 29e.