Absolute Nonsense
The Quest for Absolute Guidelines in Medicine
Evan David Rosen, M.D., Ph.D.
Assistant Professor of Medicine,
Harvard Medical School
Some
people just can't catch a break. For years now, physicians have
been telling patients that normal blood pressure is anything
below 140/90, and if you fell below this number you were A-OK
in the blood pressure department. Well, some of these folks
probably got a rude surprise if they read about a study published
in the New England Journal of Medicine. This study looked at
people with "high-normal" blood pressure (systolic
BP 130-139, diastolic BP 85-89), people that were previously
felt to be out of danger from the perils of hypertension. What
the study found was that these folks were actually still two
to three times as likely to have heart attacks or strokes than
were people with lower normal values.
This is an especially important
finding for people with diabetes, because the adverse effects
of high blood pressure tend to be magnified in these folks.
While it remains to be seen if treating people with "high-normal"
blood pressure with drugs or non-pharmacologic means (like with
diet or exercise) will help them, I suspect that the answer
will be yes when the appropriate studies on large numbers of
patients are finally completed.
But that's not what motivates
me to write about this topic. I believe that there's a hidden
truth in studies like the one cited above that will begin to
emerge over the next decade or so. I'm talking about the quest
for absolute guidelines in medicine, an approach that works
because it's the best we can do, but which I feel is philosophically
bankrupt.
Let's spell out the problem:
Doctors want to know if their methods achieve the desired results.
If it is common practice to treat high blood pressure only once
it tops 140/90, then we need to look at that practice dispassionately
and assess if there might be a better way. So, researchers look
at large numbers of people and come up with results such as
I described above. Out of these results come guidelines with
which doctors and patients can make rational choices about therapy.
This all makes sense, and there's no doubt that these guidelines
have helped a great many patients and physicians alike.
The problem with this is that
absolute guidelines based on studies in whole populations do
not take into account the fact that doctors don't treat populations.
They treat individuals. Patients are genetically distinct from
one another and surrounded by their own unique environments.
We know this in our bones--how often do you hear someone say
something like "That guy has smoked like a chimney for
thirty years and he's healthy as a horse, so how come this other
person gets lung cancer?" Or, "Bob eats everything
he wants to and stays skinny, but Ed watches his diet and still
gains weight." Individuals have very different propensities
for disease, even within the same family or community.
This problem affects every medical
condition, but the issue is very prominent in diabetes. Some
people will get diabetes if they gain just a few extra pounds,
while others will avoid the problem even if grossly obese. Similarly,
there are studies that show that if your hemoglobin A1c is below
8%, it's probably acceptable. Other studies show that there
is no hemoglobin A1c threshold for diabetic complications, which
is why we recommend that control be as tight as tolerable. The
truth is that some people will be fine with a hemoglobin A1c
of 8%, while others are not as fortunate. We just don't know
which people are which until it's too late.
And that's where I think the
biggest advances will be made in the upcoming decade or so.
We are going to learn which genes predict good and bad outcomes
in diabetes, and we are going to be able to tailor our recommendations
to individual patients. I believe that we'll be able to tell
someone that a blood pressure of 140/90 is OK for them, while
the next patient might need medication even with a pressure
of 130/80. In the meantime, absolute guidelines are worth following
because they bring at least some evidence to bear on the complex
decisions that patients and their doctors must make every day.
But the next phase is coming, and I can't wait.
Reference:
Vasan R. S., Larson M. G., Leip E. P., Evans J. C., O'Donnell
C. J., Kannel W. B., Levy D. Impact of High-Normal Blood Pressure
on the Risk of Cardiovascular Disease. New England Journal of
Medicine 345:1291-1297, Nov 1, 2001
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