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Cancer Screening (was: PAP Smear after TAH)From: Arthurfree@aol.comWed Jan 1 20:00:19 1997
In a message dated 97-01-01 18:13:18 EST, Harrison Sheld writes (in part):
> That aside, Dr. Wooley you tell me how many The evaluation of a screening test that is to be applied to entire populations is one of the more difficult things in medicine. 1)the screening test has to work, i.e. it is reasonably sensitive and specific. Otherwise the burden of working up false positives (especially if it requires testing with it's own associated morbidity) swamps the potential benefit. Remember, a false positive rate of even 1%, when applied to whole populations, will probably swamp your true positives for most disorders. 2)There has to be a significant burden of disease (this is what you are alluding to above: how much are you willing to subject all of your patients to in order to find one case a year, a decade, a career?) As you point out, this is essentially a value judgement based on cost per life impacted. 3)There needs be a significant symptom free interval (preferably measured in years!) during which the screening test is effective. 4)Effective treatment needs to be available (and should be dramatically more effective during that symptom free interval than treatment once symptoms begin). Vaginal dysplasia probably fails on the basis of sensitivity (how effective are random vaginal scrapings for cytology?), and on burden of disease (yes there's a lot of vaginal HPV, but how much dysplastic transformation/squamous cell CA do we really see?) Ask yourself: Why don't we do very many vaginal cytologies on healthy patients who haven't had a hysterectomy? Ovarian cancer has much more "burden of disease" (the other example under discussion here) but pelvic examination is not sensitive nor specific and the interval during which early treatment is curative is probably much shorter than other screening successes. Hence Dr. Wooley's questioning whether the diagnosis at pelvic only did the lady the favor of knowing she has a fatal disease for a longer period of time (yes I know early disease is surgically curable, but early disease is rarely picked up at bimanual exam). We have two roles that sometimes conflict. The first is to do the absolute best job we can for our patients individually. This is why, in select populations, physicians are (with careful counseling and little literature support) doing things that are largely unproven such as oopherectomy in familial carcinoma syndromes. What we do for populations is not always good enough for the situations in which our individual patients find themselves. The second role is to recommend what is best for our populations. The costs here, both in dollars and in grief, can be tremendous when ill thought non evidence based interventions are applied across entire populations. This (and the fact that resources are not limitless) is why statisticians look at these interventions in terms of $$ per year of life saved. This allows us to compare interventions to determine where we get the most benefit (and least risk!) for the intervention. The next place this is going to really explode is in gene therapy, where the benefits and the cost will be tremendous. It will be hard to justify spending 50K on bypass surgery for an octigenarian if that same 50K could cure a seven year old of diabetes. (Most other health care systems in the world have already made many of these explicit decisions, we in the US still labor under the impression we can do everything possible for everybody, yet is is primarily healthcare that has fueled most of the budget fights in Congress of the last four years). Tough subject, but I do believe strongly that guidelines have to be evidence based to have credibility, and that (to paraphrase John Kitzhaber) every time we (as a society) make an explicit decision to spend health care dollars on an intervention we are making an implicit decision where they will not be spent. Arthur Freeland
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