The diagnostic role of the reduced caloric intake test and
phenobarbitone treatment in
Gilbert's syndrome was evaluated. During fasting the increase in unconjugated serum
bilirubin concentration was significantly higher in patients with
Gilbert's syndrome than in normal subjects but not when compared with the increase observed in patients with acute
hepatitis, which is the clinically most relevant differential diagnosis.
Phenobarbital treatment significantly reduced the level of unconjugated serum
bilirubin in patients with acute
hepatitis or
Gilbert's syndrome, but without any difference within these two groups of patients. The reduced caloric intake test and
phenobarbital treatment seem to have low diagnostic specificity in
Gilbert's syndrome when the differential diagnosis is that of
hepatitis. The fraction of plasma unconjugated
bilirubin of total
bilirubin was significantly different in all three groups examined. The clinical diagnosis of
Gilbert's syndrome can be established with relative certainty if the patients have a mild
hyperbilirubinemia with a high fraction of unconjugated
bilirubin, normal values of liver
enzymes, and no overt signs of
hemolysis. Liver biopsy is not mandatory.