We describe a rapid, precise radiommunoassay for progesterone in 25 muL of unextracted serum. Progesterone is released from its binding protein by adding an optimal amount of cortisol, which binds to the same protein (cortisol binding globulin) as progesterone. The amount of cortisol required does not cross react with the specific progesterone antibody used. This approach considerably shortens assay time and removes a tedious and imprecise stage in the conventional assay of serum progesterone. Results correlated well (r = 0.97) with a method involving organic solvent extraction of progesterone from serum. During the two years we have used this method in a busy diagnostic endocrine laboratory, the between-assay precision (CV) for low-, medium-, and high-concentration quality control sera was 12, 7, and 9%, respectively. Data from participation in an independent external quality-control program verified the adequacies of the method.

A combined radioimmunoassay for the two thyroid hormones is described which uses 125iodine labelled triiodothyronine and 131iodine labelled thyroxine. The assay employs a double antibody separation technique and is suitable for use with unextracted serum. The results from the simultaneous assay compare very well with the results obtained in the single assays, and the discriminating power and precision of the simultaneous assay is a least as good as in the single assays.

No abstract