Testosterone testing is used to diagnose several conditions in men, women, girls, and boys. Testosterone is the main sex hormone in men, produced mainly by the testicles, and is responsible for male physical characteristics. Although it is considered to be a "male" sex hormone, it is present in the blood of both males and females. (See the "What is being tested?" section for more.)

The testosterone test may be used to help evaluate conditions such as:

• Delayed or precocious (early) puberty in boys
• Decreased sex drive in men and women
• Erectile dysfunction in men
• Infertility in men and women
• Testicular tumors in men
• Hypothalamus or pituitary disorders
• Hirsutism and virilization in girls and women

Typically, a test for total testosterone is used for diagnosis. The total testosterone test measures testosterone that is bound to proteins in the blood (e.g., albumin and sex-hormone binding globulin [SHBG]) as well as testosterone that is not bound (free testosterone).

About two-thirds of testosterone circulates in the blood bound to SHBG and slightly less than one-third bound to albumin. A small percent (less than 4%) circulates as free testosterone. Free testosterone plus the testosterone bound to albumin is the bioavailable testosterone, which can act on target tissues.

In many cases, the total testosterone test provides adequate information. However, in certain cases, for example when the level of SHBG is abnormal, a test for free or bioavailable testosterone may be performed as it may more accurately reflect the presence of a medical condition. (For more on this, see Common Questions #4.)

Depending on the reason for testing, other tests and hormone levels may be done in conjunction with testosterone testing. Some examples include:

• SHBG
• FSH, LH
• Estrogens
• DHEAS
• Prolactin
• 17-Hydroxyprogesterone
• Androstenedione

In men, the test may be ordered when infertility is suspected or when a man has a decreased sex drive or erectile dysfunction. Some other symptoms include lack of beard and body hair, decreased muscle mass, and development of breast tissue (gynecomastia). Low levels of total and bioavailable testosterone have also been associated with, or caused by, a greater presence of visceral fat (midriff or organ fat), insulin resistance, and increased risk of coronary artery disease.

In boys with delayed or slowly progressing puberty, the test is often ordered with the FSH and LH tests. Although there are differences from individual to individual as to when puberty begins, it is generally by the age of 10 years. Some symptoms of delayed puberty may include:

• Delayed development of muscle mass
• Lack of deepening of the voice or growth of body hair
• Slow or delayed growth of testicles and penis

The test also can be ordered when a young boy seems to be undergoing a very early (precocious) puberty with obvious secondary sex characteristics. Causes of precocious puberty in boys, due to increased testosterone, include various tumors and congenital adrenal hyperplasia.

In females, testosterone testing may be done when a woman has irregular or no menstrual periods (amenorrhea), is having difficulty getting pregnant, or appears to have masculine features, such as excessive facial and body hair, male pattern baldness, and/or a low voice. Testosterone levels can rise because of tumors that develop in either the ovary or adrenal gland or because of other conditions, such as polycystic ovarian syndrome (PCOS).

Males:
The normal range for testosterone levels in men is broad and varies by stage of maturity and age. It is normal for testosterone levels to slowly decline, usually after age 30. Testosterone may decrease more in men who are obese or chronically ill and with the use of certain medications.

A low testosterone level (hypogonadism) may be due to:

• Hypothalamic or pituitary disease
• Genetic diseases that can cause decreased testosterone production in young men (Klinefelter, Kallman, and Prader-Willi syndromes) or testicular failure and infertility (as in myotonic dystrophy, a form of muscular dystrophy)
• Impaired testosterone production because of acquired damage to the testes, such as from alcoholism, physical injury, or viral diseases like mumps
• Chronic disease, such as diabetes

Men who are diagnosed with consistently low testosterone levels and have related signs and symptoms may be prescribed testosterone replacement therapy by their healthcare providers. However, testosterone supplements are not approved by the Food and Drug Administration to boost strength, athletic performance, or prevent problems from aging. Use for these purposes may be harmful. For more information, see the Hormone Health Network's article: The Truth about Testosterone Treatments.

Increased testosterone levels in males can indicate:

• Testicular tumors
• Adrenal tumors that are producing testosterone
• Use of androgens (also called anabolic steroids)
• Early puberty of unknown cause in boys
• Congenital adrenal hyperplasia in babies and children

Females:
In women, testosterone levels are normally low. Increased testosterone levels can indicate:

• PCOS
• Ovarian or adrenal gland tumor
• Congenital adrenal hyperplasia

Alcoholism and liver disease in males can decrease testosterone levels. Drugs, including androgens other than testosterone and steroids, can also decrease testosterone levels.

Prostate cancer responds to androgens, so many men with advanced prostate cancer receive drugs that lower testosterone levels.

Drugs such as anticonvulsants, barbiturates, and clomiphene can cause testosterone levels to rise. Women taking estrogen therapy may have increased total testosterone levels.