A simple high-throughput enzymeimmunoassay for norethisterone (norethindrone).

A direct enzymeimmunoassay having the sensitivity required for determining norethisterone concentrations in small aliquots of plasma (10 microliter) has been developed. This assay featured a solid phase antiserum raised against a norethisterone-11 alpha-hemisuccinyl/bovine serum albumin conjugate. The antiserum was coupled to cyanogen bromide-activated magnetisable cellulose, and antibody-bound and free fractions were separated by a simple magnetic device. A norethisterone/horseradish peroxidase conjugate was used as the label; o-phenylenediamine/hydrogen peroxide being the substrate for colour development. The results obtained by this direct EIA, which allowed processing of at least 100 samples per day, were compared with those of a well-validated enzymeimmunoassay featuring solvent extraction and centrifugal separation of antibody-bound and free steroid; the results were in excellent agreement (n = 30; r greater than 0.99) suggesting the usefulness of the simple high-throughput procedure for processing the large sample numbers generated by field investigations and pharmacokinetic studies.