Questions and Answers About the
Prostate-Specific Antigen (PSA) Test
1. What is the prostate-specific antigen (PSA)
test?
The prostate-specific antigen (PSA) test measures
the level of PSA in the blood. A blood sample is drawn and the amount of PSA is
measured in a laboratory. PSA is a protein produced by the cells of the prostate
gland. When the prostate gland enlarges, PSA levels in the blood tend to rise.
PSA levels can rise due to cancer or benign (not cancerous) conditions. Because
PSA is produced by the body and can be used to detect disease, it is sometimes
called a biological marker or tumor marker.
As men age, both benign prostate conditions and
prostate cancer become more frequent. The most common benign prostate conditions
are prostatitis (inflammation of the prostate) and benign prostatic hyperplasia
(BPH) (enlargement of the prostate). There is no evidence that prostatitis or
BPH cause cancer, but it is possible for a man to have one or both of these
conditions and to develop prostate cancer as well.
Although PSA levels alone do not give doctors
enough information to distinguish between benign prostate conditions and cancer,
the doctor will take the result of this test into account in deciding whether to
check further for signs of prostate cancer.
2. Why is the PSA test performed?
The U.S. Food and Drug Administration (FDA) has
approved the PSA test for use in conjunction with a digital rectal exam (DRE) to
help detect prostate cancer in men age 50 and older. During a DRE, a doctor
inserts a gloved finger into the rectum and feels the prostate gland through the
rectal wall to check for bumps or abnormal areas. Doctors often use the PSA test
and DRE as prostate cancer screening tests in men who have no symptoms of the
disease. The FDA has also approved the PSA test to monitor patients with a
history of prostate cancer to see if the cancer has come back (recurred).
3. For whom might a PSA screening test be
recommended? How often is testing done?
The benefits of screening for prostate cancer are
still being studied. The National Cancer Institute (NCI) is currently conducting
the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial, or PLCO
trial, to determine if certain screening tests reduce the number of deaths from
these cancers. The DRE and PSA are being studied to determine whether yearly
screening to detect prostate cancer will decrease one's chance of dying from
prostate cancer.
Doctors' recommendations for screening vary. Some
encourage yearly screening for men over age 50; others recommend against routine
screening; still others counsel men about the risks and benefits on an
individual basis and encourage patients to make personal decisions about
screening.
Several risk factors increase a man's chances of
developing prostate cancer. These factors may be taken into consideration when a
doctor recommends screening. Age is the most common risk factor, with more than
96 percent of prostate cancer cases occurring in men age 55 and older. Other
risk factors for prostate cancer include family history and race. Men who have a
father or brother with prostate cancer have a greater chance of developing
prostate cancer. African American men have the highest rate of prostate cancer,
while Native American men have the lowest.
4. How are PSA test results reported?
PSA test results report the level of PSA detected
in the blood. The PSA level that is considered normal for an average man ranges
from 0 to 4 nanograms per milliliter (ng/ml). A PSA level of 4 to 10 ng/ml is
considered slightly elevated; levels between 10 and 20 ng/ml are considered
moderately elevated; and anything above that is considered highly elevated.
various factors can cause PSA levels to fluctuate, one abnormal PSA test does
not necessarily indicate a need for other diagnostic tests. When PSA levels
continue to rise over time, other tests may be indicated.
5. What if the test results show an elevated PSA
level?
A man should discuss elevated PSA test results
with his doctor. There are many possible reasons for an elevated PSA level,
including prostate cancer, benign prostate enlargement, inflammation, infection,
age, and race. If there are no other indicators that suggest cancer, the doctor
may recommend repeating DRE and PSA tests regularly to monitor any changes.
If a man's PSA levels have been increasing or if
a suspicious lump is detected in the DRE, the doctor may recommend other
diagnostic tests to determine if there is cancer or another problem in the
prostate. A urine test may be used to detect a urinary tract infection or blood
in the urine. The doctor may recommend imaging tests, such as ultrasound (a test
in which high-frequency sound waves are used to obtain images of the kidneys and
bladder), x-rays, or cystoscopy (a procedure in which a doctor looks into the
urethra and bladder through a thin, lighted tube). Medicine or surgery may be
recommended if the problem is BPH or an infection.
If cancer is suspected, the only way to tell for
sure is to perform a biopsy. For a biopsy, samples of prostate tissue are
removed and viewed under a microscope to determine if cancer cells are present.
The doctor may use ultrasound to view the prostate during the biopsy, but
ultrasound cannot be used alone to tell if cancer is present.
6. What are some of the limitations of the PSA
test?
- Detection does not always mean saving lives:
Even though the PSA test can detect small tumors, finding a small tumor does
not necessarily reduce a man's chance of dying from prostate cancer. PSA
testing may identify very slow-growing tumors that are unlikely to threaten
a man's life. Also, PSA testing may not help a man with a fast-growing or
aggressive cancer that has already spread to other parts of his body before
being detected.
- False positive tests: False positive test
results (also called false positives) occur when the PSA level is elevated,
but no cancer is actually present. False positives may lead to additional
medical procedures, with significant financial costs and anxiety for the
patient and his family. Most men with an elevated PSA test turn out not to
have cancer.
- False positives occur primarily in men age 50
or older. In this age
group, 15 of every 100 men will have elevated PSA levels (higher
than 4 ng/ml). Of these 15 men, 12 will be false positives and only
three will turn out to have cancer.
- False negative tests: False negative test
results (also called false negatives) occur when the PSA level is in the
normal range even though prostate cancer is actually present. Most prostate
cancers are slow-growing and may exist for decades before they are large
enough to cause symptoms. Subsequent PSA tests may indicate a problem before
the disease progresses significantly.
7. Why is the PSA test controversial?
Using the PSA test to screen men for prostate
cancer is controversial because it is not yet known if the process actually
saves lives. Moreover, it is not clear if the benefits of PSA screening outweigh
the risks of followup diagnostic tests and cancer treatments.
The procedures used to diagnose prostate cancer
may cause significant side effects, including bleeding and infection. Prostate
cancer treatment often causes incontinence and impotence. For these reasons, it
is important that the benefits and risks of diagnostic procedures and treatment
be taken into account when considering whether to undertake prostate cancer
screening.
8. What research is being done to improve the PSA
test?
Scientists are researching ways to distinguish
between cancerous and benign conditions, and between slow-growing cancers and
fast-growing, potentially lethal cancers. Some of the methods being studied are:
- PSA velocity: PSA velocity is based on changes
in PSA levels over time. A sharp rise in the PSA level raises the suspicion
of cancer.
- Age-adjusted PSA: Age is an important factor
in increasing PSA levels. For this reason, some doctors use age-adjusted PSA
levels to determine when diagnostic tests are needed. When age-adjusted PSA
levels are used, a different PSA level is defined as normal for each 10-year
age group. Doctors who use this method suggest that men younger than age 50
should have a PSA level below 2.5 ng/ml, while a PSA level up to 6.5 ng/ml
would be considered normal for men in their 70s. Doctors do not agree about
the accuracy and usefulness of age-adjusted PSA levels.
- PSA density: PSA density considers the
relationship of the PSA level to the size and weight of the prostate. In
other words, an elevated PSA might not arouse suspicion in a man with a very
enlarged prostate. The use of PSA density to interpret PSA results is
controversial because cancer might be overlooked in a man with an enlarged
prostate.
- Free versus attached PSA: PSA circulates in
the blood in two forms: free or attached to a protein molecule. With benign
prostate conditions, there is more free PSA, while cancer produces more of
the attached form. Researchers are exploring different ways to measure PSA
and to compare these measurements to determine if cancer is present.
- Other screening tests: Scientists are also
developing screening tests for other biological markers, which are not yet
commercially available. These markers may be present in higher levels in the
blood of men with prostate cancer.
This fact sheet was reviewed on 9/7/00
Previous FAQ |
Next FAQ
