Testosterone is the primary male hormone. It is responsible for the development of sexual characteristics, maintaining muscle mass and other body traits. Testosterone also plays a role in women, primarily as a precursor for forming estrogen. Normal testosterone levels are higher in men than women and depend on age and sexual stage of development.
Testosterone in men is primarily produced by specialized cells in the testes, with smaller amounts made in the adrenal glands. The ovaries are the main source of testosterone in women until menopause, with some contribution by the adrenal glands and soft tissues. Most of the testosterone circulating in your bloodstream is tightly attached to a transport protein, making it unavailable for activity in the tissues. Smaller amounts of the hormone are loosely attached to the protein albumin or circulating free of any protein. These forms of testosterone are biologically active, or bioavailable.
Testosterone is the major androgenic, or male category, hormone. It is required for normal sexual development in both men and women. Testosterone is responsible for development of the male external genitalia and body changes at puberty, including deepening of the voice, maturation of the reproductive organs and growth of facial and pubic hair. In women, testosterone is primarily a precursor molecule for the production of estrogen, but is also involved in growth of pubic hair at puberty. Testosterone helps maintain muscle mass and bone density in both sexes and plays a role in influencing behavior.
Male Testosterone Levels
Normal testosterone levels in males vary markedly with age. For the first few months after birth, levels range from approximately 70 to 345 ng/dL, then drop to less than 10 ng/dL until age 8 to 10, as measured at Quest Diagnostics laboratories. With the onset of puberty, levels rise gradually through the teen years to as high as 1,000 ng/dL. Normal adult values range from 250 to 1,100 ng/dL, with an individual’s testosterone level dropping slowly within this range beginning sometime after age 30. Different laboratories may have slightly different normal values depending on the test method used.
Female Testosterone Levels
Testosterone levels in women show a similar but more subdued pattern of age-related changes. Levels are highest the first few months after birth, ranging from approximately 10 to 25 ng/dL. Testosterone then drops to less than 20 ng/dL until the onset of puberty, at which time the hormone increases again to as high as 40 ng/dL. The level then stabilizes as an adult at between 2 and 45 ng/dL.
Many different medical conditions can cause an abnormal testosterone level. Testing is often performed for early or delayed puberty, erectile dysfunction or infertility in men. Irregular menses, fertility problems, unusual hair growth or other masculinizing changes may prompt testing for a woman. Testosterone test results need to be interpreted along with signs, symptoms and any other test findings with your health care practitioner.