Sensitivity of HPLC and conventional bilirubin measurements in the detection of early cholestasis.

Recent studies using very sensitive high-performance liquid chromatography (HPLC) techniques have shown that conjugated bilirubin concentrations in normal human serum are about 0.006 mg/dl, much lower than the direct-reacting bilirubin concentrations reported by typical clinical laboratory techniques (up to 0.3 mg/dl). In animal models of cholestasis, we tested the concept that HPLC measurements of true serum conjugated bilirubin would provide a more sensitive indicator of cholestasis than does the conventional measurement. Serum conjugated bilirubin was not detectable (< 0.006 mg/dl) in untreated rats and guinea pigs. After bile duct ligation, the true serum conjugated bilirubin concentration in rats was significantly elevated by 10 minutes, whereas the conventional bilirubin measurement did not become significantly elevated until 120 minutes; comparable values for the guinea pig were 30 and 240 minutes, respectively. Studies of two rat models of drug-induced cholestasis, cyclosporine A and 17 alpha-ethynylestradiol, showed that measurable levels of true conjugated bilirubin appeared in the serum of cyclosporine A-treated rats but not in the estrogen-treated animals. We conclude that true serum conjugated bilirubin concentrations measured by HPLC provide an extremely sensitive means of detecting cholestasis and that such measurements could have clinical utility in detecting very early or minimal liver dysfunction.