Hospital And Laboratory Tests Can Be Wrong
The first thing that
everyone (patients and doctors) should remember is that test results can be
This may sound rather blasphemous. We are all of us encouraged to
believe that when a machine spews out a piece of paper containing lists of
figures the result must be accurate. When results come back from the laboratory
they are regarded with the sort of reverence once accorded to messages on
tablets of stone.
But the plain fact is that most laboratory tests are
only ninety five per cent accurate.
If a test to detect a disease, whose
prevalence is one in 1,000, has a false positive rate of five per cent, there
will be 51 positive results if 1,000 people are tested. Of those 51 patients
with positive results just one will actually have the disease concerned. The
other fifty will appear to have the disease but will, in reality, be healthy.
(When considering this remarkable figure you should remember that the prevalence
rate for many diseases is much less than 1 in 1,000. A false positive rate of 5%
for a disease which affects 1 in 1,000,000 people will mean that 50,001 people
have positive results but only one of them actually has the disease concerned.)
Furthermore, that 95% accuracy rate which I have quoted is only reliable
when all the equipment in the laboratory is working absolutely perfectly - and
this is something that usually happens about once a week. As a general rule
ninety per cent accuracy is more likely.
Moreover, all this assumes that
all the technicians involved do their jobs perfectly and never make mistakes. As
has been shown many times in recent years human error can be extremely
significant - and can cause catastrophic results, much illness and many deaths.
And, of course, most patients have more than one test done. If a patient
has twenty laboratory tests done (not at all unusual) then there is a good
chance that if the patient is perfectly healthy the tests will show at least one
When doctors spot an abnormality on a test report they
immediately think of disease and then they think of treatment. There is tendency
to forget or ignore the condition of the patient.
It is easy to see from
all this that every patient going into hospital will have a good chance of being
treated for a disease he or she hasn't got.
Even when no treatment is
given there is a good chance that when a false diagnosis is made a patient's
life may be changed. One recent study showed that out of 93 children who had
been diagnosed as having heart disease - and who had lived their lives as `heart
patients' - only 17 really had heart disease.
When the first blood test
for syphilis was introduced doctors accepted it as accurate. It wasn't until
several decades later that doctors found that fifty per cent of all patients
whose blood test had shown them to have syphilis didn't have syphilis at all.
The lives of many of those patients must have been ruined quite unnecessarily.
Of course, if there is a
chance that a laboratory error may mean that a normal sample results in a `false
positive' there must also be a chance that a laboratory error may mean that an
abnormal sample results in a `false negative' reading.
negative' reading means that a patient who has symptoms and signs of an
underlying illness will be falsely reassured that there is nothing wrong with
him or her
The doctor (or the patient) may make a diagnosis and then,
when the laboratory results come back, assume that the diagnosis must be wrong.
My guess (and this is only a guess because I am not aware of any
scientific research on this subject) is that when faced with a patient with
clear cut symptoms strongly indicating an underlying problem, and a set of
`normal' laboratory results, the vast majority of doctors will allow themselves
to be influenced more by the laboratory results than by the patient's condition
and their own clinical experience.
What Is Normal?
Next, we should consider the fact that, much as the technicians might
dislike and dispute this, I do not believe that everyone fits neatly into the
range of `normal values'.
We are all different (for which we should
thank God, though if the genetic engineers get their own way and cloning becomes
commonplace this will no longer be true) and the whole concept of `normal
values' is an entirely artificial one. It should be used only as a guideline,
rather than (as it so often is) as though it were written in stone that `normal
value = healthy patient' and the corollary, `abnormal value = unhealthy
patient'. Who decides what `normal values' are? Were the samples which provided
the raw material for the `normal values' taken from healthy young patients? If
so then there must be a chance that `normal values' are different for older
There are a infinite number of reasons why a patient could
have a result outside `normal values' and yet be perfectly normal and healthy.
Too Many Tests
The problems associated with
tests and investigations are made worse by the fact that doctors undoubtedly
order far too many tests. Inevitably, this leads to more false positives - and
even more unnecessary treatment.
At least two thirds of all the tests
and investigations ordered by hospital doctors and general practitioners are
Routine blood and urine tests help doctors make a diagnosis
in only around 1% of cases.
And routine sampling for microbiological
testing is unnecessary. One survey showed that only in three per cent of cases
was the treatment given based on the result of culture and antibiotic
It is important to remember that just about every procedure
(however `minor' it might appear to be) carries a physical risk. Even sticking a
needle into a patient is potentially hazardous and the more complex the
procedure the more likely it is that something will go wrong. One study showed
that 14% of all patients who undergo invasive procedures (such as biopsies,
catheterizations or bronchoscopies) have at least one complication. Most
complications then need treatment and involve a longer stay in hospital. The
longer the patient stays in hospital the more tests are done. And on it goes.
Why Doctors Order Too Many Tests
several reasons why doctors order too many tests.
1. Tests are sometimes
ordered because they provide doctors with some protection from the risk of
litigation. A doctor who has bits of paper containing test results to
substantiate and support his selected treatment programme will probably be safe
from legal action. That is sad but it is a fact of modern life. In countries
which have lots of lawyers (you know who you are) the fear of unjustified
litigation (fed more by greed than anything else) is very real. But in the long
run it is the patients who suffer. Only the lawyers benefit. (As usual).
2. Unnecessary tests are often ordered to buy doctors time when they
don't know what is going on. Doctors who are bewildered or uncertain may simple
hide behind technology and order more and more tests in the hope that this
scatter gun approach may prove effective. The condition of the patient becomes
almost irrelevant as the doctor searches endlessly for the ever elusive
3. Some doctors practice `hot' or aggressive medicine and
insist on collecting all the possible evidence they can even when the diagnosis
is not in doubt. This type of doctor will insist on performing an endoscopy so
that he can actually see a stomach ulcer even though the patient's history (and,
maybe, an X ray) have made the diagnosis certain.
4. Doctors sometimes
order tests in order to impress their patients, their colleagues, their students
or themselves. The more esoteric the test the greater the status associated with
5. It is fairly common these days for doctors to order
unnecessary tests because they are planning to write a paper for a scientific
journal and need lots of data to fill up the pages and build up their
reputations. Most of the papers published in scientific journals are of little
or no clinical value and so yet again patients are investigated unnecessarily.
6. Doctors always undergo the first part of their training in hospital.
And in teaching hospitals students and young doctors are taught to
over-investigate. Consultants frequently berate students who haven't ordered all
the possible tests. No attempt is made to decide which tests are likely to prove
particularly helpful. No thought is given to the cost of ordering so many tests.
And no thought is given to the patient who will spend hours wandering from
laboratory to X ray department and who will end up, in consequence,
exsanguinated, radiated and exhausted. The pointlessness of all this was well
illustrated by one survey which showed that when bacteriological swabs are taken
from patients in hospital there is a two to one chance that the patient will
have been discharged before the results of the culture become available.
It is, of course, possible that the odd patient may get better before
the test results become available but the only sensible conclusion I can draw
from this survey is that in most cases the doctor in charge of the patient
regards the test that he has ordered as irrelevant to the patient's well being.
7. Finally, doctors frequently perform tests out of habit. So for
example, patients who are in hospital will often have daily tests done even
though a daily change in a specific test is unlikely to lead to a daily change
in the treatment recommended. When this happens diagnosis and investigation have
been divorced from treatment. The real risk lies in the fact that the more often
tests are performed the more likely it is that there will be one or more results
showing a new and abnormal result - and that the new, abnormal result will
inspire doctors to introduce another element to the treatment programme.
Ever since Rontgen first discovered X
rays at the end of the nineteenth century radiology has played an increasingly
important part in the average doctor's investigative armamentarium. Go into
hospital for a fairly routine operation and there is an excellent chance that
they will take at lest one X ray - even if it is only a routine X ray of your
Since 1968 medical journals around the world have frequently
carried papers pointing out that most of X rays are unnecessary, extremely
expensive, potentially hazardous and unlikely to contribute anything to a
doctor's knowledge of a patient's illness, to the way that the patient is
treated or to his or her long term health.
Doctors frequently order for
X rays as a comforting ritual rather than for any specific purpose. And, of
course, many X rays are ordered purely for legal protection.
It has been
repeatedly estimated that in most `developed' countries something like nine out
of ten X rays are unnecessary. (In the US the figure is probably even higher
I had good personal experience of the possible danger of an
X ray a few years ago. When an investigative X ray showed that I had a strangely
shaped kidney the two radiologists who had studied the X ray plates wanted me to
see a surgeon. Because of the X ray they thought I had renal cancer and urgently
needed major surgery. After I insisted on another opinion a third radiologist
immediately spotted that my abnormal kidney wasn't pathologically abnormal at
all. I just happened to have a mis-shaped kidney.
Doctors Are Dependent On Tests
Many doctors have become totally
dependent on tests of one sort or another. They feel incapable of making any
sort of clinical decision unless they have done a vast range of tests. And they
put more faith in the results they obtain from the laboratory or the X ray
department than they do in their own clinical skills.
Whenever a doctor
plans to do tests or investigations of any sort ask him how the tests or
investigations will affect the way he treats you.
If he tells you that
the test isn't going to affect the treatment (or lack of it) then the test may
not be worth having.
It is, of course, always worth remembering that
tests can cause serious health problems - and can kill.
The bottom line is that you should remember that
tests aren't as reliable, as useful or as necessary as most people think they
If you feel ill when tests have shown that there is nothing wrong
with you then you should listen to your body and ignore what may well turn out
to be `false negative' tests.
If you feel well when tests have shown
that you have a problem which needs treating just remember that there is a
chance that you are feeling well because there isn't anything wrong with you -
and that it is the laboratory test equipment rather than your body which needs
Copyright Vernon Coleman 2003