A simple, direct radioimmunoassay for salivary progesterone determination during the menstrual cycle

We describe a direct radioimmunoassay for progesterone in saliva. Results for extracted and unextracted samples agree well, showing that extraction with petroleum ether is unnecessary. The direct assay is specific and accurate, and detects as little as 2 pg of progesterone per tube (12 pmol/L). Intra- and inter-assay CVs are less than 10%. The correlation between concentrations of progesterone in saliva and plasma is good during the luteal phase of the menstrual cycle (r = 0.78, p less than 0.001, n = 76) but not during the follicular phase. We present mean concentrations of progesterone in saliva and plasma for the whole cycle in 14 normal women. Although citric acid is an effective salivary-flow stimulant, its deleterious effect on the direct radioimmunoassay precludes its use with this assay for monitoring ovulation.