this might help explain it ----------  

Q:  For checking a man's prostate, a blood test to determine the
prostate-specific antigen (PSA) has been the gold standard of the exam.
Now in the past several years, a new reading called free prostate is
being used. Just how much more accurate is this than the former PSA, and
can it also sometimes be a false positive like the PSA? It is claimed
that the free prostate can more accurately determine the possible
presence of cancer. Is this true?

A:  Yours is a complicated but important question since prostate
cancer is the leading cancer in men, with about 180,000 new cases a
year. Patients often have no symptoms and are taken by surprise when a
nodule is discovered on exam or a high PSA is found.

William See, MD, Professor and Chief of Urologic Surgery at the Medical
College of Wisconsin, explained to me that there are now at least six
different ways to look at serum PSA: total PSA, free PSA, age-adjusted
PSA, ethnically adjusted PSA, PSA velocity and PSA density. Each of
these has unique characteristics.
Some tests are more sensitive for identifying patients with cancer and
others are more specific, meaning that fewer patients without cancer
test false positive. Unfortunately, none of the available tests is
perfect. All will miss a percentage of cancers (false negative), and all
will incorrectly identify some patients who prove not to have cancer
(false positive).

Total PSA with a cut-off point above 4 ng/ml is slightly more sensitive
for the detection of patients with cancer than a free PSA cut point of
less than 25%. The more sensitive the test, the more likely that it is a
false positive. To give you an example, I have a 65-year-old patient
whose PSA went from 3 to 9 in the past year. Since he was double the
cut-off point of 4, he underwent a biopsy, which fortunately was
negative. So the abnormal PSA was a "false positive" and NOT cancer.

If his free PSA had been measured at 30%, above the 25% threshold, he
might have avoided immediate biopsy. The free PSA cut-off point of less
than 25% is more specific for a diagnosis of cancer and avoids the need
for biopsy in about 20% of patients who would otherwise undergo this
procedure based upon total PSA alone. Determining the risk of a given
patient harboring prostate cancer is not always easy and involves more
than just going by one PSA value.

Dr. Rebekah Wang-Cheng is a former Professor of Medicine at the Medical
College of Wisconsin. Her medical advice column, which answers
health-related questions from readers, also appeared in the Milwaukee
Journal-Sentinel.
 

 

knowledge is power - growing old is mandatory - growing wise is optional

The total PSA can be high for a variety of reasons.  The great majority
of such cases are due to other causes, but since early cancer can be
treated and cured, a high PSA is often considered a reason to do a
biopsy.   What is considered high has varied.  Over 4.0 ng/ml was the
previous standard, but many urologists use a lower value for younger
men.  That is because PSA tends to go up slowly for other reasons as men
age.  Your PSA is marginal for a man your age.

There are biochemical differences among different forms of PSA found in
the blood.   One form, free PSA, is a lower percent of the total when
cancer is present.   There is no specific cut off which shows cancer is
not present, but many urologists think that if the free PSA is higher
than 25 percent, it may not be necessary to do a biopsy, even if the
total PSA is high.  A free PSA lower than 10 percent certainly would
raise concern, but even in that case, it is by no means certain that
cancer is present.   Your urologist has the training and experience
necessary to weigh the importance of the total PSA and free PSA percent,
as well as other information, in deciding whether or not to do a biopsy.
  Often in cases  of very low free PSA, it may be necessary to continue
to follow the patient and do further biopsies.   That is because
sometimes the biopsy needles will just miss a small cancer.   A biopsy
plus a free PSA percent greater than 25 percent would provide greater
confidence that no cancer is present.   Fortunately, the great majority
of prostate cancers grow rather slowly, so finding one quickly is not as
important as it might be with other cancers.

PSA - A good PSA is any PSA under 4.0 that does not rise between tests.  4.0
used to be the standard at which doctors referred you to a urologist.
However, they now know that if it rises, regardless as to how low it is, two
or three tests in a row, then a problem is indicated.

Free PSA - 25% or higher is good.  10% or lower is a possible indication of
Prostate Cancer.  Between 10 and 25%, it depends.

  Your PSa sounds perfectly normal to me? Gotta be other criteria that
you're not telling us about?

PSA is Prosate Specific Antigen.  Thhe "Total" measures the actual PSA present,
nanograms per milliliter, in the blood.  Some of the PSA molecules are bound to
some enzyme, I don't know what.  Two different tests are used, one to measure
the total and the other to measure how much of it is unbound.  If more than 25%
of the PSA present is "free" ie, not bound, it is less likely that you have
prostate cancer.  PSA of less than 4 ng/ml were ignored a few years ago, but
they are getting a little more picky, especially in young men like you.