Combined radioimmunoassay of four steroids in one ml of plasma: I. Progestins.

Using partially specific antisera combined with a 1 step celite microcolumn chromatography, progesterone (P), 20alpha-hydroxypregn-4-ene-3-one (20alpha-P), 17-hydroxyprogesterone (17-P), and 16alpha-hydroxyprogesterone (16alpha-P) could be measured in the same 1 ml aliquot of plasma. The chromatographic step removed known interfering steroids and conferred specificity to the assay. After correction for recovery the sensitivities, expressed as ng/ml of plasma, were respectively: 0.04 for P, 0.03 for 20alpha-P, 0.02 for 17P, and 0.01 for 16alpha-P. Recovery experiments, using steroid-free plasma to which various amounts of each steroid were added and then measured in the assay in 12 replicates, confirmed adequate accuracy and precision. The ability to measure multiple progestogens in small volumes of plasma should permit comprehensive evaluation of the role of these steroids in health and disease.