Total Testosterone Test

Testosterone is a steroid hormone made primarily in the testes in men and the ovaries in women, with smaller amounts produced by the adrenal glands. It plays a key role in regulating metabolism, muscle mass, bone density, mood, sexual function, and overall vitality. In blood tests, “total testosterone” refers to the sum of all forms of testosterone circulating in the body: the small amount that is freely available (free testosterone), the portion loosely bound to albumin, and the majority that is tightly bound to a protein called sex hormone-binding globulin (SHBG).

Testosterone production is regulated by a feedback system involving the brain and reproductive organs called the hypothalamic-pituitary-gonadal axis. When testosterone levels drop, the brain increases production of luteinizing hormone (LH), which in turn stimulates the testes or ovaries to produce more testosterone. This system can be disrupted by a variety of factors including stress, sleep loss, insulin resistance, chronic illness, excess body fat, and certain medications.

In Men

Testosterone is often thought of as the defining male hormone, and for good reason. It helps maintain muscle mass, supports red blood cell production, enhances libido and erectile function, and contributes to energy, mood, and drive. When testosterone is low, a condition known as male hypogonadism, it can lead to reduced sexual desire, erectile dysfunction, increased body fat (especially visceral fat), loss of muscle, fatigue, low mood, and even osteoporosis.

Low testosterone is common in men with obesity, type 2 diabetes, and metabolic syndrome. In fact, testosterone and insulin resistance are tightly linked: low testosterone can worsen insulin resistance, and insulin resistance can suppress testosterone production. While testosterone naturally declines with age, this decline is often exaggerated by lifestyle factors like poor sleep, inactivity, alcohol use, and weight gain. Importantly, healthy aging men with good lifestyle habits often maintain sufficient testosterone levels well into their 60s or 70s.

Testosterone replacement therapy (TRT) can be beneficial in men who meet the diagnostic criteria, meaning they have both low blood levels and consistent symptoms. Treatment may improve sexual function, mood, energy, lean mass, and bone density. However, TRT also carries risks, including elevated red blood cell counts, acne, and potential impacts on fertility. The relationship between testosterone and prostate cancer is complex but not causal; most evidence does not support the idea that TRT increases the risk of developing prostate cancer, though monitoring is still essential.

In Women

Although testosterone is often labeled a “male hormone,” it is also critical to female health. Women produce much smaller amounts, roughly one-tenth of male levels, but those levels are essential for healthy metabolism, muscle maintenance, bone strength, mood, and sexual desire. In fact, testosterone may be especially important for women’s sense of vitality and motivation, particularly after menopause.

Too little testosterone in women can contribute to low libido, fatigue, and low mood. This is most commonly seen in women with hypothyroidism, adrenal dysfunction, or after surgical removal of the ovaries. On the other hand, too much testosterone is a hallmark of polycystic ovary syndrome (PCOS), a condition affecting up to 1 in 10 women of reproductive age. Elevated testosterone in PCOS is linked to insulin resistance, weight gain, irregular periods, fertility problems, and increased body or facial hair.

Higher-than-normal testosterone levels in women may also increase the long-term risk of type 2 diabetes and cardiovascular disease. Genetic studies show that women with higher lifelong testosterone levels tend to have higher waist circumference, worse blood sugar control, and a higher risk of heart disease. In contrast, women with very low testosterone, especially postmenopausal women, may be at increased risk for bone loss, muscle wasting, and decreased sexual well-being.