INTRODUCTION

As men age, their serum concentrations of testosterone and, to a greater extent, free testosterone, decrease. This decline is sometimes referred to as "andropause" or "late-onset hypogonadism." However, unlike menopause, where complete estrogen deficiency with known clinical consequences occurs, the decline in testosterone in aging men is modest and the possible clinical consequences have not been well-established.

Changes in body function occur in aging men that are similar to the manifestations of hypogonadism due to known disease, raising the possibility that the decline in testosterone production with aging may be a cause of these changes. The question of whether or not testosterone should be administered to elderly men is difficult to answer because it is not known whether testosterone treatment reverses the age-related decline in any function, nor is it known if testosterone treatment exacerbates any of the testosterone-dependent diseases, such as those of the prostate, to which elderly men are prone. The decline in testicular function with aging is reviewed here. Other endocrine changes seen with aging are discussed separately. (See "Endocrine changes with aging".)

CHANGES WITH AGE

Both cross-sectional and longitudinal studies demonstrate a decline in serum testosterone concentration, an increase in sex hormone binding concentration (SHBG), and a decrease in free testosterone with age. It is important to note, however, that most commercially available assays for total and free testosterone (and calculated free testosterone formulae) have both theoretical and technical limitations that hinder a clinician’s ability to reliably diagnose hypogonadism in an individual elderly man [1-3]. This issue is discussed in detail separately. (See "Clinical features and diagnosis of male hypogonadism", section on 'Which form of testosterone should be measured?'.)

Serum total testosterone — Several cross-sectional studies show a decline of serum total testosterone concentration with increasing age [4-10]. The decline, however, is relatively small. In one study, testosterone declined about 100 ng/dL (3.5 nmol/L) from age 20 to age 80 [11]. Young men exhibit a diurnal variation, with highest values at about 8 AM and lowest about 8 PM, but elderly men have little variation (figure 1) [6].

As a result of this fall, a greater percentage of elderly men have testosterone values sufficiently low to be considered hypogonadal in young men.