How to diagnose Gilbert syndrome ?

Gilbert syndrome is a genetic condition and this autosomal recessive condition is characterized by intermittent jaundice in the absence of hemolysis or liver disease.
The hyperbilirubinemia is mild. By definition, bilirubin levels in Gilbert syndrome are lower than 6 mg/dL, though most patients exhibit levels lower than 3 mg/dL. Gilbert syndrome is the resu
lt of a genetic mutation in the promoter region of a gene for the enzyme UGT1A (bilirubin–uridine diphosphate glucuronyl transferase).
A presumptive diagnosis can be made in patients with the following features:
Unconjugated hyperbilirubinemia on repeated testing
A normal complete blood count, blood smear, and reticulocyte count
Normal liver function tests (plasma aminotransferases and alkaline phosphatase concentrations)

The diagnosis is definitive in patients who continue to have normal laboratory studies (other than the elevation in plasma bilirubin) during the next 12 to 18 months. As discussed above, the diagnosis is also supported by observing a rise in the plasma bilirubin concentration following a low lipid, 400 kcal diet or after the administration of intravenous nicotinic acid. However, these provocative tests are seldom necessary in clinical practice.

Genetic testing can confirm the diagnosis in settings where there is diagnostic confusion.