PSA, DRE, PAP, RTPCR, TRUS,
and Other Diagnostic Acronyms
Last Revised May 14, 1997
[Note there may have been developments since this was written.]
Introduction |
PSA |
PSA II |
PSAV |
PSAD |
DRE |
RTPCR |
PAP |
TRUS
Introduction
An "acronym" is an abbreviation usually made up from the first letters of the words
it is being used to abbreviate. Thus, for example, FBI is an acronym
for Federal Bureau of Investigation and NFL is an acronym for the
National Football League.
Medicine is full of acronyms. In fact
there are even books which list medical acronyms so that you can look
them up if you don't know what a particular acronym stands for!
Acronyms are also common in the diagnosis and treatment of prostate
cancer, so we thought it would be a good idea if we listed some of the most
common ones here and gave a brief explanation. If you or one of your
family or friends has or thinks he might have prostate cancer, chances
are you will hear most of these acronyms in the future.
PSA
PSA stands for prostate specific antigen. The PSA test or
prostate specific antigen test has revolutionized the detection of
prostate cancer and
monitoring of the effects of treatment since the mid 1980s. On its
own, it is very probably responsible for the accurate diagnosis of
prostate cancer in millions of men worldwide. Equally, it is probably
the single most important factor in the unnecessary treatment of
some men who might well have died of old age or
many other reasons without the slightest reason to suspect that prostate
cancer was anything for them to worry about -- which they did but
shouldn't have!
The PSA test is a classic case of science providing
us with information which we do not always know how to use to our best
advantage. If you have to talk to your doctor about the results of PSA
tests (your own or a family member's), be sure that you listen very
carefully, ask a lot of questions, and do your very best to be patient
with the doctor because it may be impossible -- or at least very hard --
for him or her to give you the answers you are looking for!
A PSA test tells your doctor the level of prostate specific antigen in
your blood, just like a cholesterol test can tell your doctor the levels of
cholesterol in your blood. Using the most common type of PSA test
currently available in the USA, the average, normal, healthy,
50-year-old male is generally believed to have a PSA of less than 4.0
nanograms per milliliter of blood (4.0 ng/ml). There are a number of
reasons why any one person's PSA could be higher than that. Prostate
cancer is just one of those reasons. What the results of PSA tests do
NOT do is tell you and your doctor how to act on the results of those
tests! For more information about the value and importance of PSA and
PSA testing, see
You may also want to review the prostate cancer testing advice and consent
materials used by one group of physicians in helping patients to decide
whether they wish to have a PSA test for prostate cancer.
PSA II
The PSA II or free/total PSA test is a new type of PSA test that can be used
to help the physician discriminate between patients with relatively low standard
PSA levels (say 2.5-10.0 ng/ml) who are at greatest risk of having prostate cancer
(and therefore need a prostate biopsy), and those patients who are more likely
to have benign prostatic hyperplasia (BPH).
Basically, the PSA II test measures the amount of PSA that is free in the
blood stream, and compares it to the total free and bound PSA found in the blood
(including the PSA that is "bound" to other products in the blood). The
lower the ratio of free to total PSA, the higher the likelihood that the
patient has prostate cancer as opposed to benign prostatic hyperplasia.
Patients with a very low ratio (e.g., 0.05 or 5%) are at very high risk for
prostate cancer.
The PSA II test allows the urologist to give a non-invasive test to patients
with PSA values between 2.5 and 10.0 ng/ml who may be at risk for prostate cancer
and to determine the degree of that risk before deciding whether to
give the patient a biopsy.
PSAV
PSAV stands for PSA velocity, which is best described as the
speed at which a series of PSA values increases (or decreases) in value. Some
physicians believe that use of PSA velocity allows them to tell more
about the way prostate cancer may be developing in individual patients.
Let's say it is January 1995 and Harry, who is 68 years old and
otherwise in excellent health, has a PSA test. The doctor tells him
his PSA value is 4.2 ng/ml, and it's nothing to worry about but the
doctor suggests to Harry that he comes back for another test a year
later. In January 1996, Harry comes back for his next test. The value
is 4.4 ng/ml. Again, the doctor says its nothing to worry about but to
come again the next year. In January 1997, back comes Harry for the
third time. This year the value is 4.6 ng/ml. Each year for two
years, Harry's PSA value has increased by 0.2 ng/ml. We say that his
PSA velocity is 0.2 nanograms per milliliter of blood per year (0.2
ng/ml/yr).
PSAD
PSAD stands for PSA density. PSA density is a
measure of the concentration of PSA in a man's prostate. It depends
upon the value of his PSA and the size of his prostate. Again, like PSA
velocity, some specialists believe that PSA density can be useful in
telling how to treat individual patients.
Let's say that Bill has a
PSA value of 5.1 ng/ml. When his physician measures the volume of
Bill's prostate, the doctor calculates that it is about 50 cubic
centimeters (50 cc), which is about the same size as a large walnut.
Then Bill's PSA density is 5.1 divided by 50 = 0.102 ng/ml/cc.
DRE
DRE stands for digital rectal examination. In a digital rectal
examination the physician inserts his finger into the rectum in order
to be able to feel the size, shape, and texture of the prostate and
other nearby organs. In classical medicine, before the availability of
the modern wonders of science, the digital rectal examination was the
only way a physician could tell if there was a possible disorder of the
prostate, short of cutting you open and looking.
Over the years,
highly experienced physicians became relatively good at using digital rectal
examinations to tell whether patients had clinically important prostate
disorders. However, DRE is a "subjective" technique. In other words,
the ability to use a DRE well is all about the skill of the physician
and his or her ability to interpret what he or she feels.
The problem with using DREs to make decisions about what to do with
particular patients is that two different, experienced physicians may
think that they feel quite different things when they carry out a DRE
on the same patient. Neither of these physicians is necessarily right
or wrong in what they think. They cannot see what they are feeling and
they are doing their best to make wise decisions. Imagine trying to do
something similar. You are blindfolded and wearing a pair of plastic
gloves. Someone places two pool balls in your hands and tells you the
red one has a tiny crack in it. Now, which one is the red ball and
which is the other ball? Easy, huh? Well it would be if the crack was
big enough, but when it's a really tiny crack?
RTPCR
RTPCR stands for reverse transcriptase polymerase chain reaction.
RTPCR testing
is only a few years old. It can be used to detect minute
amounts of one of the nucleic acids which makes prostate specific
antigen. Theoretically, RTPCR is so sensitive that it is capable of
finding one piece of PSA nucleic acid in a blood sample containing a
million other pieces of nucleic acid of comparable size. This would be
wonderful if we could be sure that finding one such piece of nucleic
acid absolutely always meant that prostate cancer had escaped from the
prostate and was "metastasizing" to other sites in the body.
Unfortunately, that isn't the case. A positive reaction to an RTPCR
test can occur for all sorts of reasons in a patient who still has
clinical prostate cancer confined to the prostate. Life just isn't as
simple as we'd like it to be.
RTPCR testing is at best an investigational
technique. It is not yet approved or recommended for use in normal
clinical practice. However, if you or a friend or relation are involved
in a clinical trial of a new form of prostate therapy, RTPCR testing
may be a form of testing that is used in that trial as doctors and
scientists try to learn more about prostate cancer and which patients
most need to be treated with what types of therapy. There is little
doubt we will all continue to hear more about RTPCR testing in the
future. However, whether it will ever be possible to use RTPCR testing
as a diagnostic or prognostic test is open to considerable question.
PAP
PAP stands for prostatic acid phosphatase. Just as RTPCR is a
very new and experimental test for prostate cancer outside of the
prostate, PAP is a much older test which was in very common use before
PSA testing became possible. Today, PAP tests are relatively rare.
However, there are still reasons why doctors may think a PAP test is
valuable for a specific patient. If your doctor tells you you need a
PAP test, you should ask ask him or her to explain what the PAP test may
be able to tell that can't be learnt from PSA testing or other forms of
available test. The commonest reason for use of a PAP test is that it
may help to identify a patient with metastatic prostate cancer.
TRUS
TRUS stands for transrectal ultrasound.
TRUS is most commonly used to do two things. The first is to guide the
doctor when he or she is carrying out a technique known as a biopsy of
the prostate, when small samples of tissue are taken from the prostate
in order to make a proper diagnosis. The second is in order to try and
establish the volume of the prostate, which is important if the doctor
wants to know the PSA density. Specialists may also
use TRUS for other reasons in some prostate cancer patients or patients
suspected of prostate cancer. However, it has now been generally
agreed that TRUS has no particular value in identifying patients with
prostate cancer when used on its own or in combination with such
techniques as DRE or PSA.
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