Salivary testosterone levels and the progress of puberty in the normal boy.

Salivary testosterone (ST) levels were measured in 84 boys aged 7.3-16.2 from the Edinburgh Growth Study. The correlation coefficient between matched plasma/saliva samples was 0.88. Six samples were collected over the course of one day from 0900 to 2100 h each month in the majority of the children for 4 consecutive months. Mean daily ST levels showed a significant rise between each pubertal stage (genital (G) and pubic hair (PH]. The rise in ST became more rapid once a mean testicular volume (MTV) of 10 ml had been reached. The diurnal rhythm was assessed by individual curve fitting on the log scale and by cosinor analysis. A rhythm was present prepubertally and developed into a pattern similar to that of the adult rhythm by stage G3. The monthly rate of rise of ST was greatest at stage G4. A significant rise in ST levels was detectable immediately prior to an increase in MTV to 3 ml. This allowed earlier recognition of the clinical onset of puberty at testicular volume of 3 ml, which in this group occurred at 10.9 (SD 0.9) years. ST is a non-invasive and sensitive method for the serial monitoring of gonadal function in the prepubertal and adolescent boy.