A testosterone test checks the
level of this male
hormone (androgen) in the blood. Testosterone affects
sexual features and development. In men, it is made in large amounts by the
testicles. In both men and women, testosterone is made
in small amounts by the
adrenal glands; and, in women, by the
ovaries.
The
pituitary gland controls the level of testosterone in
the body. When the testosterone level is low, the pituitary gland releases a
hormone called
luteinizing hormone (LH). This hormone tells the
testicles to make more testosterone. See a picture of the
pituitary gland.
Before
puberty, the testosterone level in boys is normally
low. Testosterone increases during puberty. This causes boys to develop a
deeper voice, get bigger muscles, make
sperm, and get facial and body hair. The level of
testosterone is the highest around age 40, then gradually becomes less in older
men.
In women, the ovaries account for half of the testosterone in
the body. Women have a much smaller amount of testosterone in their bodies
compared to men. But testosterone plays an important role throughout the body
in both men and women. It affects the brain, bone and muscle mass, fat
distribution, the vascular system, energy levels, genital tissues, and sexual
functioning.
Most of the testosterone in the blood is bound to a
protein called sex hormone binding globulin (SHBG). Testosterone that is not
bound ("free") can also be checked if a man or a woman is having sexual
problems.
The health professional taking a sample
of blood will:
Wrap an elastic band around your upper arm to stop the flow of
blood. This makes the veins below the band larger so it is easier to put a
needle into the vein.
Clean the needle site with alcohol.
Put the needle into the vein. More than one needle stick may be
needed.
Attach a tube to the needle to fill it with blood.
Remove the band from your arm when enough blood is
collected.
Put a gauze pad or cotton ball over the needle site as the needle
is removed.
The blood sample is taken from a vein in
your arm. An elastic band is wrapped around your upper arm. It may feel tight.
You may feel nothing at all from the needle, or you may feel a quick sting or
pinch.
There is very little chance of a problem from
having blood sample taken from a vein.
You may get a small bruise at the site. You can lower the chance
of bruising by keeping pressure on the site for several minutes.
In rare cases, the vein may become swollen after the blood sample
is taken. This problem is called phlebitis. A warm compress can be used several
times a day to treat this.
Ongoing bleeding can be a problem for people with bleeding
disorders. Aspirin, warfarin (Coumadin), and other blood-thinning medicines can
make bleeding more likely. If you have bleeding or clotting problems, or if you
take blood-thinning medicine, tell your doctor before your blood sample is
taken.
The testosterone level for a postmenopausal woman is
about half the normal level for a healthy, nonpregnant woman. And a pregnant
woman will have 3 to 4 times the amount of testosterone compared to a healthy,
nonpregnant woman.
Normal free testosterone
levels in men range from 44 to 244
pg/mL (0.68 to 3.76
pmol/L). In women, the free testosterone level may
range from 0.6 to 9.2 pg/mL (0.01 to 0.14 pmol/L).
High values
In men, a high level of testosterone may be caused by cancer of
the
testicles or
adrenal glands.
In boys younger than 10, a high level of testosterone may mean
early (precocious) puberty, a tumor in the testicles, or an abnormal adrenal
gland.
In women, a high level of testosterone may be caused by cancer
of the ovaries or adrenal glands or
polycystic ovary syndrome (PCOS).
Low values
In men or boys who have gone through puberty, a low level of
testosterone may be caused by a problem with the testicles, such as slow
development of, an injury to, or a lack of testicles. It can also be caused
from treatment with the female hormone
estrogen, a problem with the
pituitary gland, or many long-term (chronic)
illnesses.
In women, a low level of testosterone may be caused by an
underactive pituitary gland,
Addison's disease, loss of
ovary function through disease or surgery, and some
medicines (such as
corticosteroids or estrogen).
Reasons you may not be able to
have the test or why the results may not be helpful include:
Taking medicines such as estrogen (including birth control
pills), testosterone, corticosteroids, digoxin (Lanoxin), spironolactone
(Aldactone), or
barbiturates.
Having
hyperthyroidism. This can raise sex hormone binding
globulin (SHBG) levels.
Hypothyroidism can lower SHBG levels.
Taking medicines to treat prostate cancer.
Taking medicines that raise
prolactin levels, such as certain seizure
medicines.
Most of the testosterone in the blood is bound to a protein
called sex hormone binding globulin (SHBG). "Free" testosterone may be checked
when conditions that can increase SHBG levels, such as obesity or
hyperthyroidism, are present.
The levels of other hormones made by the pituitary gland, such as
follicle-stimulating hormone (FSH) and
luteinizing hormone (LH), may be checked to see
whether a low testosterone level is caused by problems with the testicles or
ovaries or the pituitary gland. For more information, see the medical tests
Luteinizing Hormone and
Follicle-Stimulating Hormone. A really high level of
LH and a low level of testosterone often means that the testicles or ovaries
are not working properly. A low LH level and a really low or high testosterone
level may mean a problem with the pituitary gland.
For women, medicines such as birth control pills or
corticosteroids may lower levels of testosterone. Oral estrogens used for
hormone replacement therapy can also lower
testosterone levels.
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
Fischbach FT, Dunning MB III, eds. (2004).
Manual of Laboratory and Diagnostic Tests, 7th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis:
Mosby.
Shifren JL, et al. (2006). Testosterone patch for the
treatment of hypoactive sexual desire disorder in naturally menopausal women:
Results from the INTIMATE NM1 study. Menopause: The Journal of the North American Menopause Society, 13(5): 770–779. [Erratum in
Menopause, 14(1): 157.]
Somboonporn W, et al. (2007). Testosterone for peri-
and postmenopausal women. Cochrane Database of Systematic Reviews (4).
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