Serum total and free testosterone level of Japanese men: a population-based study

There has never been a large scale population-based study of serum levels of total testosterone (TT) and free testosterone (FT) in Japanese men.

We determined serum levels of TT and FT of 1120 Japanese men aged 40-79 years using radioimmunoassay (RIA), as a part of a population-based longitudinal study of aging. Of these, sex hormone binding protein (SHBG) was also measured by RIA in 471 men. For the latter group, the calculated free testosterone (cFT) was determined by a formula using serum level of albumin, TT and SHBG.

The mean +/- 2 SD of TT, FT and cFT were 513 +/- 326 ng/dL (187-839 ng/dL), 13.2 +/- 7.8) pg/mL (5.4-21.0 pg/mL) and 77.0 +/- 43.4 pg/mL (33.6-120.4 pg/mL), respectively. While TT did not relate to age, FT and cFT decreased with age. FT in the 40-49 years age group was 15.1 +/- 8.4 pg/mL (6.7-23.5 pg/mL), in the 50-59 years age group was 13.9 +/- 6.8 pg/mL (7.1-20.7 pg/mL), in the 60-69 years age group was 12.0 +/- 6.6 pg/mL (5.4-18.6 pg/mL) and in the 70-79 years age group was 11.5 +/- 7.0 pg/mL (4.5-18.5 pg/mL). FT significantly correlated with cFT (Spearman's r = 0.803). The correspondence rates were 92.3% at the mean -1 SD and 98.7% at the mean -2 SD level.

We determined the mean and standard deviation of TT, FT and cFT in Japanese men aged 40 years or older. It is supposed that FT determined by RIA would be useful for diagnosing partial androgen deficiency of aging males.