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Decline of serum levels of free testosterone in aging healthy Chinese men

Objective. To investigate the age-related change of serum androgen levels in healthy men and to define a cut-off value of serum testosterone for the diagnosis of androgen deficiency in the aging male. Method. 1080 healthy men aged 20 to ⩾70 years old were enrolled in Beijing, Shanghai, Xian and Chongqing. Luteinizing hormone (LH), follicle-stimulating hormone (FSH), total testosterone (T), calculated free testosterone (cFT), sex hormone binding globulin (SHBG), 17beta-oestradiol (E2), the T/LH ratio, and T/SHBG as a free testosterone index (FTI) were all determined. Results. Serum total T did not significantly decline, but the cFT, T/LH and FTI progressively decreased with aging. To determine androgen deficiency, the 10th percentile value of men <40 years was defined as the lower cut-off value for cFT, T/LH or FTI, which were 0.3 nmol/L, 2.8 nmol/IU, and 0.4 nmol/IU respectively. With the median value of cFT of men aged between 20 and 49 years as the criterion, the level of cFT was lower in 2.82% of men from 40 to 49 years, in 19.53% from 50 to 59 years, in 22.57% from 60 to 69 years, and in 33.19% of men ⩾70 years. Taking the above value of cFT as the cut-off point, the prevalence of androgen deficiency in men 40–49 years was 13.0%, 31.8% in men 50–59 years, 30.1% in men 60 to 69 years, and 46.7% in men >70 years. Conclusions. (i). While serum total T values do not decline with aging, the levels of cFT gradually decline with aging; (ii) when using the value of cFT of the 10th percentile of men aged 20 to 39 years as the cut-off point, the prevalence of androgen deficiency was <15% before the age of 50 years, and about 30% thereafter, approaching 45% after the age of 70 years; and (iii) in this study the values of T/LH paralleled those of cFT closely; therefore, T/LH could serve as a surrogate for cFT.