Reproducibility of saliva progesterone measured by immunoassay compared to liquid chromatography mass spectrometry

Immunoassay overestimates progesterone in blood, but no studies have tested whether this occurs in saliva. We measured progesterone in saliva using immunoassay and mass spectrometry. We tested the immunoassay for cross reactivity with dehydroepiandrosterone sulfate (DHEA-S) and 17α-hydroxyprogesterone (17α-OHP). Progesterone was significantly higher in immunoassay compared to mass spectrometry. Immunoassay progesterone levels increased in when incremental levels of 17α-OHP standard was added. This effect was not observed with the addition of DHEA-S. Research using salivary progesterone immunoassay techniques should be wary, particularly with individuals taking steroid supplementation or with high levels of progesterone metabolites.