Direct radioimmunoassay of progesterone in human plasma

A direct method has been described which enables a specific assay of progesterone without extraction in human plasma or in other material containing corticosteroid binding globulin (CBG). When using 20 microliter of plasma per tube, a sensitivity of 6 pg/tube, or 0.3 ng/ml can be achieved. The precision and accuracy are comparable to those observed in methods involving extraction. The described method is particularly suitable for routine assays.