A prostate-specific antigen (PSA) test measures the amount of
prostate-specific antigen in the blood. PSA is
released into a man's blood by his
prostate gland. Healthy men have low amounts of PSA in
the blood. The amount of PSA in the blood normally increases as a man's
prostate enlarges with age. PSA may increase because
of inflammation of the prostate gland (prostatitis) or
prostate cancer. An injury, a digital rectal exam, or
sexual activity (ejaculation) may also briefly raise PSA levels.
Prostate cancer often grows very slowly, without causing major problems.
Detecting prostate cancer early and treating it may prevent some health
problems and reduce the risk of dying from the cancer. But some treatments for
prostate cancer can cause other problems, such as being unable to control
urination (incontinence) or erection problems (erectile dysfunction). Some men may choose not to have
a PSA test or treat prostate cancer if it is detected. For example, a man older
than age 75 who has no bothersome symptoms of prostate cancer may choose not to
treat the cancer if it is found, so he would not need a PSA test.
The prostate-specific antigen (PSA) test
is done to:
Screen men for prostate cancer. Experts
disagree on the usefulness of PSA testing as a screening tool for prostate
cancer. If a PSA test is used for screening, it is usually done for men older
than age 50 or for those at high risk for prostate cancer, such as men with a
family history of prostate cancer, or for African-American men who have a
higher chance of developing cancer than other men. Since other common medical
conditions, such as prostatitis, can cause high PSA levels, a prostate
biopsy is needed to confirm a diagnosis of
cancer.
Check if cancer may be present when results from other
tests, such as a
digital rectal exam, are not normal. A PSA test does
not diagnose cancer, but it can be used along with other tests to determine if
cancer is present.
Watch prostate cancer and see if treatment is
working. If PSA levels increase, the cancer may be growing or spreading. PSA is
usually not present in a man who has had his prostate gland removed. A PSA
level that rises after prostate removal may mean the cancer has returned or has
spread.
How To Prepare
Before you have a prostate-specific
antigen (PSA), tell your doctor if you have had a:
Test to look at your bladder (cystoscopy) in the past several
weeks.
Tube (catheter) inserted into your bladder to
drain urine recently.
Do not ejaculate during the 2 days before your PSA blood
test, either during sex or masturbation.
Talk to your doctor about
any concerns you have regarding the need for the test, its risks, how it will
be done, or what the results will mean. To help you understand the importance
of this test, fill out the
medical test information form(What is a PDF document?).
How It Is Done
The health professional taking a sample
of your 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.
Put pressure to the site and then a
bandage.
How It Feels
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.
Risks
There is very little chance of a problem from
having a 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.
Results
A prostate-specific antigen (PSA) test
measures the amount of
prostate-specific antigen in the blood. Normal values
may vary from lab to lab.
Normal
Because normal PSA levels seem to increase
with age, age-specific ranges may be used. But the use of age-specific ranges
is controversial, and some doctors prefer to use one range for all ages. For
this reason, it is important to discuss your test results with your
doctor.
A follow-up test that measures free prostate-specific
antigen (free PSA) may be used to see if a prostate biopsy should be done to
check for cancer. The lower a man's free PSA level, the more likely he is to
develop prostate cancer.
Free prostate-specific antigen (fPSA)
Percent free PSA
Probability of cancer
More than 25%:
8%
20%–25%:
16%
15%–20%:
20%
10%–25%:
28%
0%–10%:
56%
What Affects the Test
Reasons you may not be able to
have the test or why the results may not be helpful include:
Recent sexual activity (ejaculation) or a
cystoscopy.
Large doses of medicines, such as cyclophosphamide
(Cytoxan, Neosar), diethylstilbestrol, and methotrexate for cancer
treatment.
The medicine finasteride, such as Proscar or Avodart,
which is used to prevent further enlargement of the
prostate gland in men with BPH.
What To Think About
When combined with a
digital rectal exam, the prostate-specific antigen
(PSA) test increases the chance of detecting prostate cancer. For more
information, see the medical test
Digital Rectal Examination (DRE).
A PSA
level within the normal ranges does not mean that prostate cancer is not
present. Some men with prostate cancer have normal PSA levels.
The American Cancer Society (ACS) advises doctors about when to
offer the PSA test and DRE:
Offer these tests to men ages 50 and older
who are expected to live more than 10 years.
Offer these tests to
men starting at age 45 if they are at high risk for prostate cancer. This group
includes African-American men and men who have a father, brother, or son who
was diagnosed with prostate cancer before age 65.
Offer these tests
to men starting at age 40 if they are at an even higher risk for prostate
cancer. This group includes men who have several close relatives who had
prostate cancer at an early age.
Before any tests, it is important for men younger than 75 to
talk with a doctor about the pros and cons of PSA testing.
Men
younger than 75 who have long-term medical problems or who are expected to live
less than 10 years are not likely to benefit from testing.
Some experts do not advise yearly testing. They
say the high rate of
false-negative and
false-positive results and the costs and risks of
further tests outweigh the benefits of yearly screening tests.
Experts disagree about the type of testing that is appropriate if
the PSA level is high. The decision may depend on:
Results of your digital rectal
exam.
Results of any PSA tests you have had in the past. If your
PSA level gets higher in a short amount of time, follow-up testing may be
recommended.
Your age and health.
The costs and risks
of more tests and treatments.
Other prostate tests are being evaluated to
determine how well they tell the difference between prostate cancer and benign
prostatic hypertrophy.
The prostate-specific antigen density
(PSAD) test compares the PSA value to the size of the prostate gland. The size
of the prostate is measured using transrectal ultrasound
(TRUS).
The PSA velocity test is a measure of how rapidly PSA
levels increase over time. PSA levels increase more rapidly in men with
prostate cancer and more slowly in men with prostate enlargement (benign
prostatic hypertrophy).
A complexed prostate-specific antigen (cPSA) test may help show
if a prostate biopsy should be done. This test measures the amount of a protein
made in the prostate (cPSA) that is found in the blood.
References
Other Works Consulted
Chernecky CC, Berger BJ (2008). Laboratory Tests and Diagnostic Procedures, 5th ed. St. Louis:
Saunders.
Fischbach FT, Dunning MB III, eds. (2009).
Manual of Laboratory and Diagnostic Tests, 8th ed.
Philadelphia: Lippincott Williams and Wilkins.
Pagana KD, Pagana TJ (2006). Mosby’s Manual of Diagnostic and Laboratory Tests, 3rd ed. St. Louis:
Mosby.
U.S. Preventive Services Task Force (2008).
Screening for Prostate Cancer: Clinical Summary of a U.S. Preventive Services Task Force Recommendation. Also available online:
http://www.ahrq.gov/clinic/uspstf/uspsprca.htm.
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