Testosterone is the major male hormone, 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
Testosterone in men is primarily produced by specialized cells in the testes, with smaller amounts made in the adrenal glands, according to the Mayo Clinic Laboratories. 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 any activity in the tissues. Smaller amounts of the hormone are loosely attached to albumin or circulating free of any protein, making them biologically active, or bioavailable.
Effects of Testosterone
Testosterone is the major androgenic, or male category, hormone, and is required for normal sexual development in both men and women according to the Merck Manuals Online Medical Library. Testosterone is responsible for development of the male external genitalia, and body changes at puberty, including deepening of the voice, maturation of 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 also helps maintain muscle mass and bone density in both sexes and play 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 75 to 400 ng/dL, then drop to less than 20 ng/dL until around age 10 years, as measured at Mayo Clinic Laboratories. With the onset of puberty, levels rise gradually through the teen years to as high as 1200 ng/dL. Normal adult values are then from 240 to 950 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 in women shows a similar, but more subdued, pattern of age-related changes. Levels are highest the first few months after birth, ranging from 20 to 80 ng/dL. As in males, 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 75 ng/dL. The level then stabilizes as an adult at between 8 and 60 ng/dL.
Abnormal Levels
Many different medical conditions can result in abnormal testosterone levels. Testing is often performed for early or delayed puberty, erectile dysfunction or infertility in men, according to MedlinePlus. Irregular menses, unusual hair growth or other masculinizing changes in women might also lead to testing. Results need to be interpreted along with signs, symptoms and any other test findings with your health care practitioner.
