Sunday, September 15, 2019

Should High Blood Pressure be Treated?



In last week's post, I promised an explanation why many screening and medical treatments offer so little benefit to individual patients.   If you invest the time to digest last week's post and the post before you now, then you will be equipped with new understanding that will enable you to make much better medical decisions.  In accordance with this blog's mission, this is truly a 'peek behind the curtain'.  I grant you that these 2 posts are a little wonky, but try to stay focused.  

Here is the main reason that ordinary people – and even some medical personnel – become confused on this issue.  Studies that assess screening tests and medical treatments are often performed on very large groups of patients.  The reason for this is that smaller studies, for reasons I cannot fully explain here, are simply not felt to be sufficiently reliable.   This is why the Food and Drug Administration would never grant approval of a new medicine based on favorable results from small studies.   If a benefit or a failure is shown in a high quality study with hundreds or thousands of participants, the results will be highly credible.   It was large studies, for example that demonstrated that blood pressure control prevented serious complications. 

Here is the key point.  When a medical benefit is established in a large study, this benefit applies to a large population of people.   When this medical test or treatment is later applied to an individual patient in a doctor’s office, the benefit that this person receives may be miniscule.   This reality is not appreciated by nearly all patients I have treated in nearly 3 decades.  If a patient reads about a study that concludes that losing excess weight will cut the risk of stroke by 30%, the patient is likely to make 2 false assumptions:

He overestimates his risk of stroke.

He overestimates the true risk reduction of losing 10 lbs.

If his risk of stroke is already very low, then reducing it by 30% offers almost no benefit.  Follow the next example.


Will Lowering My BP Save My Life?

Assume a study of 5000 patients with high blood pressure demonstrates that lowering blood pressure 10%, can halve the risk of developing a heart attack.  This sounds like a game changer, but not to an individual patient, such as any person reading this.  The benefit is derived from studying a large population.   Assume that without treatment that 100 patients of the 5000, or 2%, would suffer a heart attack in 10 years.  With blood pressure treatment, only 50 patients would suffer this outcome, a 50% decrease in the adverse event.   Wouldn’t it be true that an individual patient would also have a 50% risk of developing a heart attack?  Yes, but let’s play this out.

A patient comes to the doctor with modest high blood pressure and no other cardiac risks. The patient has read about the landmark study that concludes that treatment would halve his heart attack rate.  Let’s assume, that this person’s risk of developing a heart attack in 10 years is 3%.  That means that this individual already has a 97% chance of staying well without any treatment.  Treating this patient would lower his risk of a heart attack from 3% to 1.5%, representing the 50% benefit we have been discussing.  So, with treatment, he now has a 98.5% probability of avoiding a heart attack.  Would someone enthusiastically take lifelong blood pressure medicine for an additional 1.5% protection when he already was 97% in the clear?   Would most of us welcome this return on investment?  I am not even considering the costs of many of these treatments and the potential side effects.   

When large studies’ benefits are applied to individuals, the benefits calculate out very differently. However, treating hundreds of thousands, or millions of people with elevated blood pressure would save many of them simply because we are dealing with large numbers of people.  A percentage point or two of a million people is a respectable number.  That’s why it makes sense to treat many diseases from a public policy standpoint.  The point is that each individual only enjoys a very modest benefit. 

I hope that readers have found this post – and the blog overall – to offer a very high return on investment.   Your comments are always welcome. 


3 comments:

Nora said...

Excellent blog post. It's a bit of a shame that science and math are so under appreciated by all. Don't even get me started on the whole mammogram and early detection math... Mammograms don't save lives. Self-awareness and treatment save lives.

Rich Maranoff M.D. said...

and if your mild hypertension is treated and you are normotensive, should you still be considered hypertensive when being fit into other guidelines, eg. heart attack, stroke, Afib, etc. And to add insult they are always lowering the goalposts and creating sick people out of well ones. Big Pharma loves this. Excellent post.

Michael Kirsch, M.D. said...

Thanks so much to these commenters for having the focus and fortitude to get through two tough posts! I hope you'll return to the blog from time to time and share your thoughts.

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