Accuracy of A Direct Progesterone Immunoassay

Background: Beyond the established role of serum progesterone measurement in the luteal phase of menstrual cycle to confirm recent ovulation, it is also increasingly used to detect premature luteinization during in vitro fertilization (IVF) hyperstimulation, where late follicular phase increase in serum progesterone is reportedly associated with adverse pregnancy outcomes. Virtually all serum progesterone measurements in clinical and IVF practice use direct, nonextraction immunoassays, often in multiplex, high-throughput platform assays optimized for high, postovulatory, midluteal phase serum progesterone concentrations. However, the performance of direct progesterone immunoassays for smaller increases is not established.Methods: We studied 254 women undergoing IVF hyperstimulation with serum progesterone around the time of human chorionic gonadotropin (hCG) administration, measured in each sample by a direct progesterone immunoassay (Beckman Coulter Access) and by LC-MS.Results: Immunoassay overestimated serum progesterone in almost every sample with an increasingly high variability and deviation at lower concentrations (immunoassay <5 nmol/L, equivalent to LC-MS <2 nmol/L).Conclusions: Immunoassay consistently overestimates serum progesterone levels so that low measurements (immunoassay <5 nmol/L) are too inaccurate to be used quantitatively. The utility of higher serum progesterone measurements by immunoassay and serum progesterone and other steroids measured by multiplex LC-MS profiling in predicting IVF pregnancy outcomes warrants further investigation. There is a need for caution in clinical diagnosis of premature luteinization based on increased late follicular phase serum progesterone measurements using direct progesterone immunoassay that consistently overestimates low serum progesterone concentrations.