Serum testosterone levels using the radioimmunoassay method in healthy Japanese male volunteers.

Aim:  The objective of the present study was to measure serum free and total testosterone values using the radioimmunoassay (RIA) method in healthy Japanese male volunteers with no current diseases.
Methods:   Two hundred and fifty-one healthy men who had no medical illness and received no current medical treatment were selected from 405 male volunteers. Free and total testosterone were measured in blood samples using the RIA method.
Results:   Free but not total testosterone significantly decreased with age. Mean free testosterone values from morning blood samples for each age decade from the 20s to the 70s were 17.0, 14.6, 12.5, 10.6, 8.9 and 8.5 pg/mL, respectively. Mean total testosterone values from morning blood samples for each age decade from the 20s to the 70s were 4.7, 4.2, 4.4, 4.2, 4.2, 4.0 and 4.0 ng/mL, respectively. The rates of healthy volunteers that fell within the standard reference ranges for free and total testosterone were 97% and 97%, respectively. However, 19% of the total testosterone values were considered to indicate hypogonadism according to the International Society for the Study of the Aging Male (ISSAM) criteria (<3.17 ng/mL). Conclusions:  Our data corresponded to the standard reference ranges of Japanese men but not the ISSAM criteria. It may be more appropriate to establish a standard reference range for serum testosterone for individual countries. (Reprod Med Biol 2006; 5: 37-41).