Testosterone
Serum testosteroneA testosterone test measures the amount of the male hormone, testosterone, in the blood. Both men and women produce this hormone.
The test described in this article measures the total amount of testosterone in the blood. Much of the testosterone in the blood is bound to a protein called sex hormone binding globulin (SHBG). Another blood test can measure the "free" testosterone. However, this type of test is often not very accurate.
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How the Test is Performed
A blood sample is taken from a vein. The best time for the blood sample to be taken is between 7 a.m. and 10 a.m. A second sample is often needed to confirm a result that is lower than expected.
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How to Prepare for the Test
The health care provider may advise you to stop taking medicines that may affect the test.
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How the Test will Feel
You may feel a slight prick or sting when the needle is inserted. There may be some throbbing afterward.
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Why the Test is Performed
This test may be done if you have symptoms of abnormal male hormone (androgen) production.
In males, the testicles produce most of the testosterone in the body. Levels are most often checked to evaluate signs of abnormal testosterone such as:
- Early or late puberty (in boys)
- Infertility, erectile dysfunction, low level of sexual interest, thinning of the bones (in men)
In females, the ovaries produce most of the testosterone. The adrenal glands can also produce too much of other androgens that are converted to testosterone. Levels are most often checked to evaluate signs of higher testosterone levels, such as:
- Acne, oily skin
- Change in voice
- Decreased breast size
- Excess hair growth (dark, coarse hairs in the area of the moustache, beard, sideburns, chest, buttocks, inner thighs)
- Increased size of the clitoris
- Irregular or absent menstrual periods
- Male-pattern baldness or hair thinning
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Normal Results
Normal measurements for these tests:
- Male: 300 to 1,000 nanograms per deciliter (ng/dL) or 10 to 35 nanomoles per liter (nmol/L)
- Female: 15 to 70 ng/dL or 0.5 to 2.4 nmol/L
The examples above are common measurements for results for these tests. Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or test different specimens. Talk to your provider about the meaning of your specific test results.
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What Abnormal Results Mean
Certain health conditions, medicines, or injury can lead to low testosterone. Testosterone level also naturally drops with age. Low testosterone can affect sex drive, mood, and muscle mass in men.
Decreased total testosterone may be due to:
- Chronic illness
- The pituitary gland does not produce normal amounts of some or all of its hormones
- Problem with areas of the brain that control hormones (hypothalamus)
- Low thyroid function
- Delayed puberty
- Diseases of the testicles (trauma, cancer, infection, immune, iron overload)
- Benign tumor of the pituitary cells that produce too much of the hormone prolactin
- Too much body fat (obesity)
- Sleep problems (obstructive sleep apnea)
- Chronic stress from too much exercise (overtraining syndrome)
Increased total testosterone level may be due to:
- Resistance to the action of male hormones (androgen resistance)
- Tumor of the ovaries
- Cancer of the testes
- Congenital adrenal hyperplasia
- Taking medicines or drugs that increase testosterone level (including some supplements)
References
Rey RA, Josso N. Diagnosis and treatment of disorders of sexual development. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 119.
Rosenfield RL, Barnes RB, Ehrmann DA. Hyperandrogenism, hirsutism, and polycystic ovary syndrome. In: Jameson JL, De Groot LJ, de Kretser DM, et al, eds. Endocrinology: Adult and Pediatric. 7th ed. Philadelphia, PA: Elsevier Saunders; 2016:chap 133.
Swerdloff RS, Wang C. The testis and male hypogonadism, infertility, and sexual dysfunction. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 221.