Diminished testosterone production is one of many potential causes of infertility in males.^5,6 Low testosterone concentrations can be caused by testicular failure (primary hypogonadism) or inadequate stimulation by pituitary gonadotropins (secondary hypogonadism). Since men with hypogonadism often have high SHBG levels, the measurement of free or bioavailable testosterone has been advocated when total testosterone levels are normal in men with symptoms of androgen deficiency.⁶ Significant physiological changes occur in men as they age, in part due to a gradual decline in testosterone levels.^7,8 It is generally accepted that the principal cause of this age-related decrease in testosterone production is testicular failure, although diminished gonadotropin production may play a role.⁹ By 75 years of age, the average male testosterone drops to 65% of average level in young adults. “Andropause” is a term that has been used to refer to the constellation of symptoms associated with the age-related decline in testosterone production in men.^9,10

Much smaller amounts of testosterone and dihydrotestosterone are produced in women than in men.^4,5 Weaker adrenal androgens and ovarian precursor molecules including androstenedione, DHEA, and DHEA sulfate can have significant androgenic effects in women. The ovary and adrenal glands produce some testosterone but the majority of the testosterone in women is derived from the peripheral conversion of other steroids. Often, the first sign of testosterone excess in women is the development of male pattern hair growth, which is referred to as hirsutism.^5,11,12 It should be noted that some women experience hair growth similar to that caused by increased testosterone due to racial or genetic causes and not due to excessive androgens. Measurement of the testosterone may help to distinguish racial or genetic causes of hirsutism from the abnormal pathology, particularly in women with mixed ethnic backgrounds. Women with more excessive testosterone levels may also experience virilization, with symptoms including increased muscle mass, redistribution of body fat, enlargement of the clitoris, deepening of the voice, and acne and increased perspiration. These women can also suffer from androgenic alopecia, the female equivalent of male pattern baldness.

Many women with slowly progressive androgenic symptoms are diagnosed as having polycystic ovary syndrome (PCOS).^12,13,14 PCOS is relatively common, affecting approximately 6% of women of reproductive age.⁴ Women with this complex syndrome experience symptoms of androgen excess associated with menstrual abnormalities and infertility. Most women with the syndrome have polycystic ovaries that can be detected by ultrasonography although this finding is not essential for diagnosis.^5,6,11 Chronic anovulation experienced by patients with PCOS increases their risk of developing endometrial cancer. Women with PCOS are often overweight and are likely to suffer from insulin resistance putting them at increased risk for developing type 2 diabetes mellitus.^4,13 Obesity and insulin resistance can result in acanthosis nigricans, a skin condition that is characterized by hyperpigmented, velvety plaques of body folds.⁴ Lipid abnormalities, including decreased high-density lipoprotein cholesterol levels and elevated triglyceride levels as well as impaired fibrinolysis, are seen in women with PCOS.¹³ Cardiovascular disease is more prevalent and women with PCOS have a significantly increased risk for myocardial infarction.¹³