The nicotinic acid provocation test and unconjugated hyperbilirubinaemia.

It has been suggested that the nicotinic acid provocation test is useful in the diagnosis of Gilbert's syndrome. We compared the response to intravenous nicotinic acid of patients with Gilbert's syndrome and with chronic liver disease. There was no significant difference in the mean rise in unconjugated serum bilirubin between the two groups. A sensitivity of 70% and specificity of 60% were obtained. All of 5 patients with chronic liver disease and a raised fasting unconjugated serum bilirubin had positive tests. We suggest that the nicotinic acid test is positive in unconjugated hyperbilirubinaemia regardless of cause. It is of no value in differentiating Gilbert's syndrome from liver disease.