INFLUENCE OF ANTISERA ON THE ESTIMATIONS OF NORETHISTERONE AND LEVONORGESTREL

The specificity of six different antisera for norethisterone (NET) and ten different antisera for levonorgestrel (LNG) were studied. These antisera had varying degrees of cross-reactivities with the metabolites of the respective steroids. The antisera obtained from the same animal showed a trend towards higher cross-reactions with the length of the immunization period. Animal variation also seemed to be a major factor in deciding the specificity of antisera. Using these antisera radioimmunoassays (RIAs) for NET and LNG were standardized which fulfilled the necessary criteria for reliability. When NET and LNG concentrations were determined in pooled plasma, collected from women taking contraceptives containing the respective steroids, it was observed that the variation in the cross-reactivities of the metabolites with the antiserum used, had negligible effect on NET estimates, whereas they influenced the LNG estimates. © 1979.