Gilbert's Syndrome: A benign condition characterized by a mild increase in unconjugated bilirubin due to a partial deficiency of the enzyme uridine diphosphate glucuronyltransferase (UGT). It is often discovered incidentally during routine blood tests and is more common in males.

Hemolysis: Conditions that lead to the breakdown of red blood cells can cause an increase in bilirubin levels. This could be due to various reasons such as autoimmune hemolytic anemia, hereditary spherocytosis, or glucose-6-phosphate dehydrogenase (G6PD) deficiency.
Drug-induced hyperbilirubinemia: Certain medications can cause an elevation in bilirubin levels, either by increasing bilirubin production (e.g., through hemolysis) or by affecting its metabolism and excretion.

Hemolytic disease of the newborn (if applicable): Though more relevant in neonates, it's crucial to consider in the appropriate context, as it can lead to severe jaundice and kernicterus if not promptly treated.
Crigler-Najjar Syndrome: A rare but serious condition that affects the metabolism of bilirubin, leading to very high levels of unconjugated bilirubin. Type I is more severe and can lead to kernicterus, while Type II is less severe but still requires monitoring.

Dubin-Johnson Syndrome: A rare genetic disorder characterized by chronic jaundice due to an inability to secrete conjugated bilirubin into the bile. It typically presents with a distinctive black liver due to the accumulation of epinephrine metabolites.
Rotor Syndrome: Similar to Dubin-Johnson Syndrome, it is a benign condition that affects the secretion of bilirubin glucuronides into the bile, leading to a mild increase in conjugated bilirubin levels. It is differentiated from Dubin-Johnson Syndrome by the lack of liver discoloration.
Thyroid disorders: Both hypothyroidism and hyperthyroidism can affect bilirubin levels, though this is less common and usually seen in conjunction with other clinical signs of thyroid dysfunction.