Also known as:Total Testosterone; Free Testosterone; Bioavailable Testosterone
Related tests:FSH, LH, SHBG, DHEAS, Estradiol (see Estrogens), Dihydrotestosterone (DHT), Gonadotropin-releasing Hormone, Semen Analysis, Anti-Mullerian Hormone, Androstenedione
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Why Get Tested?
To detect an abnormal testosterone level in males and females; in males, to help diagnose the cause of erectile dysfunction or the inability of your partner to get pregnant (infertility); in females, to help diagnose the cause of masculine physical features (virilization), infertility, or polycystic ovary syndrome (PCOS); in children, to help determine the cause of genitals that are not clearly male or female (ambiguous genitalia) or delayed or early puberty
When to Get Tested?
- For males, when you may be infertile or are unable to get or maintain an erection; when you are a boy with either early or delayed sexual maturity (puberty)
- For females, when you have male traits, such as a low voice or excessive body hair (hirsutism), when you have abnormal uterine bleeding, do not menstruate (amenorrhea), or are infertile
A blood sample drawn from a vein in your arm; a morning sample is preferred.
Test Preparation Needed?
How is it used?
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:
When is it ordered?
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).
What does the test result mean?
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
In women, testosterone levels are normally low. Increased testosterone levels can indicate:
- Ovarian or adrenal gland tumor
- Congenital adrenal hyperplasia
Is there anything else I should know?
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.
What is being tested?
Testosterone is the main sex hormone (androgen) in men. It is responsible for male physical characteristics. Although it is considered to be a "male" sex hormone, it is present in the blood of both men and women. This test measures the level of testosterone in the blood.
Testosterone is mainly produced by special endocrine tissue (the Leydig cells) in the male testicles. It is also produced by the adrenal glands in both males and females and, in small amounts, by the ovaries in females.
In males, testosterone stimulates development of secondary sex characteristics, including enlargement of the penis, growth of body hair, muscle development, and a deepening voice. It is present in large amounts in males during puberty and in adult males to regulate the sex drive and maintain muscle mass. In women, testosterone is converted to estradiol, the main sex hormone in females.
Testosterone production is stimulated and controlled by luteinizing hormone (LH), which is manufactured by the pituitary gland. Testosterone works within a negative feedback mechanism: as the testosterone level increases, LH production decreases, which slows testosterone production; decreased testosterone causes increased production of LH, which in turn stimulates testosterone production.
Testosterone levels are diurnal, peaking in the early morning hours (about 4:00 to 8:00 am), with the lowest levels in the evening (about 4:00 to 8:00 pm). Levels also increase after exercise and also decrease with age.
About two-thirds of testosterone circulates in the blood bound to sex-hormone binding globulin (SHBG) and slightly less than one-third bound to albumin. A small percent (less than 4%) circulates as free testosterone. The free plus the albumin-bound testosterone is the bioavailable fraction, which can act on target tissues.
In many cases, measurement of total testosterone provides a healthcare practitioner with 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, see Common Questions #4.)
How is the sample collected for testing?
A blood sample is taken by needle from a vein in the arm.
NOTE: If undergoing medical tests makes you or someone you care for anxious, embarrassed, or even difficult to manage, you might consider reading one or more of the following articles: Coping with Test Pain, Discomfort, and Anxiety, Tips on Blood Testing, Tips to Help Children through Their Medical Tests, and Tips to Help the Elderly through Their Medical Tests.
Another article, Follow That Sample, provides a glimpse at the collection and processing of a blood sample and throat culture.
Is any test preparation needed to ensure the quality of the sample?
No test preparation is needed.
- If I have a low testosterone level, will taking supplemental testosterone help?
Maybe. Testosterone supplements, either with gels, patches or injections, can raise testosterone levels. They may help to relieve some symptoms and/or prevent muscle and bone loss that occurs with aging in men; however, this has not been definitively proven. There is concern that testosterone replacement therapy may exacerbate preexisting Prostate cancer, but no evidence of causing cancer. There are label warnings that testosterone administration may result in possible increased risk of heart attack and stroke. Although men with erectile dysfunction may have low testosterone, in many cases testosterone administration does not improve the symptoms because there are other underlying conditions. Therefore, consult a healthcare practitioner for a medical evaluation and consultation to determine if this is the right therapy for you. Also read the Hormone Health Network's infographic: The Truth About Testosterone Therapy.
- I am a woman, so why do I need a testosterone test?
Women's bodies also produce testosterone but in small amounts. It is needed for hormonal balance and to help women's bodies to function normally. If your body is producing too much testosterone, you may have more body hair than average, have abnormal or no menstrual periods, or be infertile. A testosterone test, in conjunction with measuring other hormone levels, can help your healthcare provider to understand what is causing your symptoms.
- Is the amount of hair directly proportional to the amount of testosterone in my body?
The amount, color, and texture of hair is largely determined by genetics. Studies have shown a proportional relationship of testosterone levels to the amount of body hair. The hair growth response to testosterone differs in different parts of the body. Hence, in some men, for example, testosterone promotes hair growth in the abdomen and back while hair growth is suppressed in the scalp, leading to male pattern baldness. Genetics plays a major role in the expression of the enzyme 5-alpha reductase, which converts testosterone to the hair-altering compound dihydrotestosterone, leading to a family tendency towards balding. The drug finasteride (Propecia®) inhibits the action of 5-alpha reductase and can reverse male pattern baldness in some men.
- What are free testosterone and bioavailable testosterone?
Testosterone is present in the blood as "free" testosterone (less than 4%) or bound testosterone (~98%). The latter may be loosely bound to albumin (about one-third), the main protein in the fluid portion of the blood, or bound to a specific binding protein called sex hormone binding globulin or SHBG (about two-thirds). The percentages in the three fractions varies greatly. The binding between testosterone and albumin is not very strong and is easily reversed, so the term bioavailable testosterone (BAT) refers to the sum of free testosterone plus albumin-bound testosterone.
It is suggested that bioavailable testosterone represents the fraction of circulating testosterone that readily enters cells and better reflects the bioactivity of testosterone than does the simple measurement of serum total testosterone. Also, varying levels of SHBG can result in inaccurate measurements of bioavailable testosterone. Decreased SHBG levels can be seen in obesity, hypothyroidism, androgen use, and nephritic syndrome (a form of kidney disease). Increased levels are seen in cirrhosis, hyperthyroidism, and estrogen use. In these situations, measurement of free testosterone may be more useful.
© 2017 American Association for Clinical Chemistry, republished from Lab Tests Online.*
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