The utility of rifampin in diagnosing Gilbert's syndrome

The aim of this study was to evaluate the effect of rifampin (the "rifampin test") on serum bilirubin in patients with and without Gilbert's syndrome.

We conducted a clinical trial in which the effect of rifampin on serum bilirubin level in 15 patients with Gilbert's syndrome was compared with 10 patients without Gilbert's syndrome (controls) in a General Internal Medicine/Primary Care clinic of a Veterans Affairs medical center. Each participant underwent a "rifampin test," i.e., bilirubin measurement at baseline and 2, 4, and 6 h after the administration of 900 mg of rifampin. Measurements included complete blood count, blood chemistry including liver panel tests (ALP, AST, LDH, and albumin) along with total serum bilirubin levels. Ten patients with Gilbert's and nine control patients had haptoglobin level measured at baseline and 6 h after the administration of rifampin.

While fasting, the mean rise in total serum bilirubin at 2, 4, and 6 h after the administration of rifampin, respectively, was 0.5, 0.7, and 0.7 mg/dl (analysis of variance, p < 0.001) in control patients and 0.6, 1.0, and 1.1 mg/dl (p < 0.001) in the study patients. In 15 fed subjects (six control and nine study), the mean rise in total serum bilirubin at 2, 4, and 6 h, respectively, was 0.3, 0.5, and 0.6 mg/dl (p < 0.001) in controls and 0.5, 1.0, and 1.2 mg/dl (p < 0.001) in study subjects. In the fasting state, rise in total serum bilirubin to >1.9 mg/dl distinguished patients with Gilbert's syndrome from those without at 2, 4, and 6 h (sensitivity 100%, 93%, and 93%; specificity 100%, 100%, and 100% at 2, 4, and 6 h, respectively). In the nonfasting state, rise in total serum bilirubin to > 1.5 mg/dl at 4 and 6 h after rifampin administration distinguished the two groups (sensitivity 90% and 100%; specificity 100% and 100%, respectively).

Rifampin increases total serum bilirubin levels in patients with and without Gilbert's syndrome. On fasting for 12 to 24 h, an absolute increase of bilirubin to >1.9 mg/dl 2 to 6 h after the administration of 900 mg of rifampin distinguishes patients with Gilbert's syndrome from those without it. In the nonfasting state, an increase in total serum bilirubin to > 1.5 mg/dl 4 to 6 h after the administration of rifampin distinguishes persons with Gilbert's syndrome from those without it.