Salivary and plasma bound and "free" testosterone in men and women

Paired samples of blood and saliva from 37 men and nine women throughout the menstrual cycle were measured for testosterone by radioimmunoassay and free testosterone by equilibrium dialysis. There was a highly significant correlation between plasma and salivary testosterone, with a correlation coefficient r = 0.71 (p = less than 0.001). In men, free testosterone constituted 78% of salivary testosterone but only 4% of plasma testosterone; mean +/- SE salivary testosterone was 193.7 +/- 6.7 pg/ml compared to plasma testosterone of 5,140 +/- 298.0 pg/ml. Salivary testosterone decreased significantly from a morning (0800 hours) level of 208 +/- 7.5 to an evening (1800 hours) level of 174 +/- 8.4 pg/ml (p = less than 0.001) (n = 23). Similarly, plasma testosterone was significantly higher in the morning (6,584 +/- 472 pg/ml) than in the evening (5,571 +/- 357 pg/ml) (p = less than 0.005) (n = 25). Free testosterone in saliva and plasma also showed significantly higher morning than evening levels. The coefficients of variability for hourly changes (0900 to 1800 hours) in salivary testosterone and free testosterone were 13.6% and 16.7% compared to 12.7% and 20.9% for plasma testosterone and free testosterone, respectively. In women, salivary testosterone during the proliferative phase of the menstrual cycle was 108.3 +/- 5.8 pg/ml, and it increased significantly to 130.5 +/- 6.0 pg/ml in the secretory phase (p = less than 0.02). Our findings indicate that measurements of salivary testosterone reflect plasma testosterone and may be a useful noninvasive method of assessing levels of testosterone.