The diagnosis has traditionally been established based on mild unconjugated hyperbilirubinemia. High levels of bilirubin can be triggered by factors such as dehydration, fasting, intercurrent disease, menstruation. Liver histology fails to show any apparent differences. Patients often exert a normal complete blood count and reticulocyte count, aminotransferases and alkaline phosphatase concentrations are within normal range and the only marginal difference is unconjugated hyperbilirubinemia on repeated testing. Your physician may test the condition by asking you to follow a low lipid, 400 kcal diet, but this test is rarely performed. The latter however, gives rise in the plasma bilirubin concentration.
The diagnosis is definitive in patients who continue to have genetic testing in the next 12-18 months. Genetic testing is currently available in many laboratories worldwide.