Determination of serum progesterone levels using a direct 125I-radioimmunoassay

A new conventional simple and direct 125I-radioimmunoassay (RIA) for serum progesterone is described. In comparison with the classical tritiated assays which are preceded by extraction, the assay is more simple, less time-consuming, less subject to error and hence less expensive. In normal cycling females the serum progesterone range during the follicular phase was 0.9 to 5.5 ng/ml (mean 2.5 ng/ml). Levels above 12 ng/ml occurring during the luteal phase are indicative of adequate luteal function. The actual progesterone levels assayed with this method are significantly greater than those found using the classical tritiated technique, and the reasons for this discrepancy are discussed. The assay is also capable of being used to assess the response to treatment for infertility, thus indicating that, in spite of the higher values obtained, there is no impairment in diagnostic sensitivity.