What type of hyperbilirubinemia is Gilbert's syndrome characterized by?

Gilbert's syndrome is characterized by unconjugated hyperbilirubinemia due to a genetic defect in the enzyme responsible for conjugating bilirubin in the liver, specifically a deficiency in the activity of UDP-glucuronosyltransferase. This enzyme is responsible for converting unconjugated (indirect) bilirubin into its conjugated (direct) form, which can then be easily excreted in bile and urine.

In Gilbert's syndrome, because of this enzymatic deficiency, there is an accumulation of unconjugated bilirubin in the bloodstream. This condition is typically asymptomatic and is often found incidentally during routine blood tests that reveal elevated levels of bilirubin, mostly unconjugated.

The other options do not correctly describe Gilbert's syndrome. Conjugated hyperbilirubinemia would indicate a problem with excretion or an obstruction of bile, while mixed hyperbilirubinemia could imply both conjugated and unconjugated components due to various liver diseases. Direct hyperbilirubinemia suggests that there is an increase in the conjugated form of bilirubin, which is not the case in Gilbert's syndrome. Thus, unconjugated hyperbilirubinemia is the hallmark of this benign condition.