Use of serum bile acids in the identification of vinyl chloride hepatotoxicity

Most previous studies proposing serum bile acids as indicators of hepatic function have been performed in hospitalized patients in whom overt symptomatic liver disease was present. The ability of fasting levels of serum bile acids to identify mild, clinically inapparent chemical liver injury in an occupational setting was compared with that of indocyanine green clearance and routine biochemical liver tests in 67 asymptomatic chemical workers in whom liver biopsies had been performed for medical indications. Histologically, 15 were found to have chemical liver injury, 27 had nonchemical liver disease, and 25 were normal. Two serum bile acids, cholylglycine and conjugates of cholic acid, were determined by radioimmunoassay, using 466 "normal" males from the same worker cohort as a reference range. The geometric mean concentrations of cholylglycine in patients with chemical liver injury, patients with nonchemical liver disease, and normal subjects were 47.9, 19.1, and 20.0 micrograms/dl, respectively (p = 0.036 by analysis of variance). Conjugates of cholic acid showed similar differences (p = 0.027), as did indocyanine green clearance with mean half-life of 4.2, 3.2, and 3.3 minutes in the three biopsy subgroups, respectively (p = 0.043). Such differences were not observed for biochemical liver tests. The fasting level of serum bile acids provided high specificity but lower sensitivity in the detection of all types of liver disease. However, serum bile acids and indocyanine green clearance provided a higher specificity and sensitivity for chemical liver injury than for nonchemical liver disease. An index of average exposure to vinyl chloride was significantly greater in the subgroup with chemical liver injury than in the other two groups, further supporting the association of chemical type injury with impaired anion uptake. These data identify the fasting level of serum bile acids as a clinically usable indicator of early chemical injury in chemically exposed asymptomatic worker populations with liver dysfunction. Further investigation is needed in other occupational hepatotoxic environments to determine if this association is limited to vinyl monomer type injury.