You, and the U.S. Preventive Services Task Force

Evidence, Absence, and Actionable Intelligence

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Much of the time, I write about the lifestyle interventions to which the greater portion of my time, effort, and career are directed.  Those allocations are, I believe, very well justified for a Preventive Medicine specialist, since the right application of lifestyle as medicine could prevent fully 80% of all major chronic disease and premature death.  That’s a rather luminous promise, and ample cause for a career-long crusade.

  So I am engaged, but that’s a tale for other days and other columns.

In clinical practice, the emphasis of prevention is, of course, on individual patients rather than changing the world.  That emphasis is expressed in so-called “clinical preventive services.”  As the name suggests these are discrete clinical interventions, or services, directed at disease prevention.  For the most part, they come in two domains, and three basic categories.  The domains are primary and secondary prevention.  The categories are immunization and chemoprophylaxis; counseling; and screening.

Primary prevention is an effort to prevent a disease before it ever begins.  That’s what immunization (or vaccination) is intended to do: prevent an infection from occurring at all.  Chemoprophylaxis is related, and involves the use of a medication to prevent a disease.  The daily use of aspirin to prevent a heart attack is an example.

  Even as I am writing this, there is a new recommendation for the use of daily aspirin to prevent colon cancer as well.

The lines can blur, however.  Sometimes an effective vaccine reduces the severity of an infection, such as influenza, rather than preventing it altogether.  Sometimes aspirin fails to prevent a heart attack, but diminishes the damage to heart muscle, and the complications.

Counseling, which involves clinicians in the time-honored role of teacher or coach (the origins of the word “doctor” in Latin mean “to teach”), can be directed at either primary or secondary prevention.  So, for instance, nutrition counseling might be all about staying healthy.  Counseling for prudent alcohol intake might be directed at preventing the consequences of an established, but early alcohol problem.

Screening is the quintessential illustration of secondary prevention, an effort directed at finding a problem that already exists, but finding it early enough to prevent its serious consequences.  Cancer screening is recommended when early detection improves treatment options and outcomes as compared to detection later, when progression of a cancer makes it obvious.

Most medical societies with skin in the particular game offer recommendations in the area of clinical preventive services.  Cardiologists, for instance, and the major organizations in their field, issue guidance about use of aspirin.

  The American Urological Association offers guidelines related to prostate cancer.

The source of expert guidance I recommend to you, and your physician, is the U.S. Preventive Services Task Force.  The Task Force is a group of carefully selected, highly qualified, multidisciplinary experts whose only job on the panel is to review the scientific evidence scrupulously, and follow where it leads.  They are independent of government, and obligated to avoid any conflicts of interest.  Unlike other specialty organizations, they are not writing about a field in which they have a vested interest, giving them a uniquely impartial perspective.

The result is a unique authority as well.  Major insurers, both public and private, routinely base reimbursement policies directly on the recommendations of the Task Force, which are clearly summarized using a letter grade.

When the Task Force recommendations are decisively in favor of a service, such as screening for colon cancer, their influence fosters widespread coverage.  When their recommendation is decisively against, such as using electrocardiograms to screen for heart disease in low-risk people, their influence appropriately discourages frivolous care and its attendant costs.

But there is a very important caveat to all of this, and it was impressed upon me by an email message I received only yesterday, after I had already committed to writing this column.  My correspondent has had skin cancer, and is screened routinely for more of the same.  She wanted to know why the Task Force does not recommend for skin cancer screening, and why, as a result, such screening is not reliably reimbursed by third party payers.

My answer was that the Task Force relies on a very high standard of evidence, generally randomized trials, with a clear indication of the net effect (benefit or harm) at the population level.  This makes their recommendations very reliable when they are decisively for an intervention.  It makes them very reliable when they are decisively against, too, with an important proviso: advances in testing or treatment could make such guidance obsolete at any time.  If, for instance, we learned how to differentiate reliably between prostate cancers destined to progress and those destined to remain indolent, it would require a change in the guidance.  The Task Force is aware of this, and updates routinely, but in any given moment, the official guidance could lag behind the latest advance.

This, however, is not the issue with skin cancer screening.  Often, there is simply an absence of the high-quality evidence the Task Force requires to reach closure.  Sometimes, no large, long-term intervention trials have been done.  Sometimes, the results of several such trials are at odds with one another.  Sometimes, the net effect of a service on the health of the population is unclear.

These impasses result not from evidence of absent benefit, but from a relative absence of evidence.   The former is proof that something doesn’t work; the latter is lack of proof that something does.  Often, the conclusion reached by the Task Force is that the evidence they need to reach a conclusion is absent.  They thus decide…not to decide.

In the area of health policy, this is reasonable.  We can agree, for instance, that we are uncertain about the population-level effects of skin cancer screening.  But this does not work at the level of an individual patient, who has an either/or choice: to be screened, or not to be screened.  That is the question.  While public policy can wait for future evidence to reach closure, a patient in the office today needs closure today.

This is why, despite authoritative guidelines, a solid doctor/patient relationship is essential to good care.  Much of the decision-making must be personalized, and that is best done by a doctor and patient who know and trust one another, and think things through together.  The Task Force may function as the veritable bible of clinical preventive services, but they do not know you.  You do, and your doctor does (or should).

This is also why I favor reimbursement policies that provide the benefit of coverage in areas of current doubt.  When a service is known to be useless, it should be discouraged.  But when the evidence is unclear, coverage should support the customized decision making and reasonable choices of doctors and patients working in the context of uncertainty.

I encourage you to familiarize yourself with the Task Force recommendations that pertain to you and your family.  Your doctor should know about them, but there is no reason not to take matters into your own hands as well.  They are a treasure trove of actionable intelligence; put them to use accordingly. 

Bear in mind, however, the important distinction between absence of evidence, and evidence of absence.  You will have to populate those gaps with informed decisions customized to you.


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