A simple radioimmunoassay for estriol 3-sulfate in pregnancy plasma without deconjugation

A highly specific anti-estriol 3-sulfate antiserum was treated with 50% ammonium sulfate, and the crude globulin fraction was coupled to CNBr-activated Sepharose-4B. Addition of 0.1M Tris-HC1 buffer (pH 8.3) containing 0.1M glutamine to the solution of antigen-antibody enabled assaying without solvent-extraction or chromatography to remove endogenous interference. Subsequently, a direct radioimmunoassay using [6,7-3H]-estriol 3-sulfate as a radioactive ligand without deconjugation has been established and applied to the determination of estriol 3-sulfate levels in pregnancy plasma. The increasing plasma levels of estriol 3-sulfate are correlated with estriol levels over the period of gestation. The mean values of sulfated estriol concentration (A) in late pregnancy plasma were approximately 7 times as high as unconjugated estriol (B), but individual ratios of A to B showed considerable variability.