Genetic variants in UGT1A1 may cause reduced or absent UGT1A1 enzymatic activity, resulting in conditions associated with unconjugated hyperbilirubinemia including Gilbert syndrome and Crigler-Najjar syndromes types I and II. Gilbert syndrome is the most common hereditary cause of increased bilirubin. This assay also helps in identifying individuals who are at increased risk of adverse reactions with drugs that are metabolized by UGT1A1 including Irinotecan, Atazanavir, Nilotinib, Pazopanib and Belinostat.