The nicotinic acid test in the evaluation of unconjugated hyperbilirubinemia.

In 42 young adults with Gilbert's syndrome and in 9 patients with inactive, well-compensated liver cirrhosis the peroral nicotinic acid test was performed. Of the 13 parameters tested, the groups differed significantly in the sum of total and unconjugated serum bilirubin concentrations, respectively, during the test; in the difference between the maximal and initial concentrations of total and unconjugated bilirubin; in the retention of total bilirubin at the third, fourth and fifth hour of the test; and in the size of the area under the curve of unconjugated bilirubin increase. However, due to considerable overlap, no single parameter could reliably differentiate among all persons with Gilbert's syndrome and cirrhotics. The nicotinic acid test is neither necessary for the diagnosis of Gilbert's syndrome nor can it reliably differentiate between this condition and severe organic liver disease. Yet, it does supply valuable information about the readiness of the organism to develop or enhance hyperbilirubinemia following a defined stimulus.