ProScreen test both for the Prostate Specific Antigen (PSA) and for free PSA
What is the Prostate Specific Antigen?
The prostate specific antigen (PSA) is a
substance produced by certain cells in the prostate gland. PSA is a protein and
is a part of semen that causes it to liquefy (keeps the semen watery). Most of
the PSA produced by the prostate gland is carried out of the body in semen, but
a very small amount escapes into the blood stream.
How is PSA measured?
PSA is tested in the blood. Since the
amount of PSA in the blood is very low, detection of it requires a very
sensitive type of technology (monoclonal antibody technique).
The PSA protein can exist in the blood by
itself, or it can join with other substances in the blood. When it is by
itself, it is known as free PSA. When it is joined with other substances, it is
known as bound or complexed PSA. Total PSA is the sum
of free and bound forms. This is what is measured as the standard PSA test.
What are normal results for the PSA test?
The most frequent value used as the
highest normal level is 4 ng/mL (nanograms per milliliter).
However, since the prostate gland generally increases in size and produces more
PSA with increasing age, it is normal to have lower levels in young men and
higher levels in older men. Age-specific PSA levels are as follows (age group,
upper normal): (40 - 49, 2.5), (50 - 59, 3.5), (60 - 69, 4.5), (70 - 79, 6.5).
The use of age-specific PSA ranges for the detection of prostate cancer is
controversial. Not all studies have agreed that this is better than simply
using a level of 4 ng/mL as the
highest normal value.
How is PSA used to detect prostate cancer?
The PSA test is used in two distinctly
different ways with respect to detecting prostate cancer. It can be used in men
who are not known to have the disease (screening or diagnostic test) and those
who are known to have the disease (tumour marker or monitoring test).
As a screening or diagnostic test, an
abnormal result will usually require additional testing. Levels above 4 ng/mL but less than 10 ng/mL are suspicious. However, most men who have this level
of abnormality will actually not have prostate cancer. As levels increase above 10 ng/mL, the probability
increases dramatically.
As a tumour marker or monitoring test, an
abnormal result indicates recurrence of prostate cancer following initial
therapy. For example, if the prostate gland is surgically removed
(prostatectomy), and all of the cancer is contained within the gland, then the
PSA should drop to zero. If on subsequent testing the PSA test is positive and
shows increasing levels, then not all of the cancer was successfully removed
and it has spread.
What other conditions can cause an abnormal PSA level?
Other diseases that affect the prostate
gland can cause an elevated PSA. The most frequent problem is known as benign prostatic hypertrophy
(enlargement) or hyperplasia (BPH). This condition is due to an increase in
the size of the prostate gland that typically occurs with aging. Infection of
the prostate gland (prostatitis)
is another relatively common affliction that can also cause an abnormal
elevation of PSA. Other conditions include poor blood supply to the prostate
gland, instrumentation of the urethra (drainage tube from the bladder), urinary
retention, and prostate biopsy.
What is the free PSA test?
Most of the PSA protein released into the
blood becomes attached to other blood proteins. The PSA that does not become
attached is known as free PSA and can be measured. It has been found that the
level of free PSA is decreased in men who have prostate cancer compared to
those with benign conditions. The exact level depends upon which test the
laboratory uses, but generally less than 10% free PSA is suggestive of cancer.
This test is most helpful when the usual PSA test is between 4 and 10 ng/mL.
What are the limitations of the PSA test?
A few percent of prostate cancers do not
produce detectable increases in the blood PSA, even with advanced disease. Many
early cancers will also not produce enough PSA to cause a significantly
abnormal blood level. It is therefore important not to rely only on blood PSA
testing.
The most useful additional test is a
physical prostate examination by a doctor known as the digital rectal exam (
PSA Test At A Glance
The PSA
test is a blood test.
The PSA
test can be used to suggest the presence of or monitor prostate cancer.
The PSA
test can be abnormal with benign enlargement and infection of the prostate
gland.
The PSA
test can be elevated with other conditions that irritate the prostate gland.
