SAT-018 Differences In Assay Results Can Be Traced To The Metabolism Of Administered Progesterone In Women Taking Progesterone Supplementation

Hormone replacement therapy (HRT) is useful in peri- and post-menopausal women to alleviate symptoms using a variety of HRT strategies to deliver estrogen either orally or transdermally and oral progesterone. However, the various assays available to measure steroid hormones have rapidly improved, evolving from antibody-based testing to highly specific tandem mass spectrometry methods. Recently, we observed mismatches in the results of anonymized patient samples submitted for progesterone measurement using immunoassays (IA) and tandem mass spectrometry (MS) methods with progesterone results being lower in the MS assays and higher in the IA measured on the same samples. We hypothesized that these differences could reflect the accumulation of progesterone metabolites in patients following the administration of supplemental oral progesterone such that the IA was unable to distinguish progesterone from its metabolites. To explore this hypothesis, we conducted a prospective observational study to examine progesterone levels in cycling premenopausal women (on no therapy, n = 2), premenopausal women (receiving oral progesterone, n = 4), and postmenopausal women (on progesterone replacement, n = 10). Women provided a baseline (8 AM) serum measurement, and +1, +2, and +4 hour samples. All subjects took their progesterone dose immediately after the baseline sample. In spontaneously cycling premenopausal women, the progesterone measurements of IA and MS (0, 1, 2 and 4 hours) were highly correlated. In all progesterone supplemented individuals, the MS baseline progesterone levels were lower than the IA values. Following administration of progesterone, progesterone levels in both methods rose, peaking at 1-2 hours after administration and then falling. The magnitude of this increase varied between methods and individuals receiving the same dose of supplemental progesterone. However, the magnitude of increase was always higher in the IA assay. MS analysis of these samples showed the presence of the progesterone metabolites, 20 alpha- and 5 alpha-dihydroprogesterone. The presence of these two metabolites and other as-yet-untested metabolites most likely explains the different progesterone values measured in the IA and MS assays in progesterone supplemented individuals. These findings reinforce the need to recognize the capabilities of the assays used and the kinetics with which administered progesterone is metabolized in order to guide patient dosing.