tag:blogger.com,1999:blog-4519234397783312626.post2817694774965023768..comments2023-10-09T11:42:57.305-04:00Comments on Healthcare, etc.: Why medical testing is never a simple decisionMarya Zilberberghttp://www.blogger.com/profile/16080475886113209344noreply@blogger.comBlogger14125tag:blogger.com,1999:blog-4519234397783312626.post-6047582350775532602010-12-22T12:40:11.362-05:002010-12-22T12:40:11.362-05:00Here's why I performed an unnecessary medical ...Here's why I performed an unnecessary medical test. http://bit.ly/5k81VjMichael Kirsch, M.D.https://www.blogger.com/profile/07555280388086931097noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-29177920370104070462010-12-18T18:09:03.841-05:002010-12-18T18:09:03.841-05:00I recommend reading Dr. Nissen's 2008 editoria...I recommend reading Dr. Nissen's 2008 editorial on a study of CT angiography. <br />Nissen, Limitations of Computed Tomography Coronary Angiography, J. Am. Coll. Cardiol. 2008;52;2145-2147.<br />http://content.onlinejacc.org/cgi/content/short/52/25/2145Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-76393508563051378182010-12-18T11:16:38.132-05:002010-12-18T11:16:38.132-05:00I think the default position in cardiology is inte...I think the default position in cardiology is intervention, not in all of medicine please<br /><br />Statistics are great and everything, and I'm all for a Bayesian discussion, but testing is often done because of defensive medicine and perverted incentivisation/conflicts of interest, and a few bad apples see below<br /><br /><br /><br /><br />http://www.nytimes.com/2010/12/06/health/06stent.html?_r=1&pagewanted=2<br /><br />Ads<br />St Joseph Stent Lawyers<br />Reviewing Cases for Unneeded<br />Stent Implants. Learn More.<br />Virginia<br />www.YouHaveALawyer.comAnonymousnoreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-43007414153717274702010-12-17T09:23:48.080-05:002010-12-17T09:23:48.080-05:00Thanks for clarifying, Sanjay. As you can imagine,...Thanks for clarifying, Sanjay. As you can imagine, you know this literature a lot better than I do.<br /><br />As for using other test characteristics, I will at some point talk about them as well here. My sense is that the PPV and NPV may be the most intuitive values for both clinicians and patients, but certainly LR+ and LR- are not that difficult to grasp. As for AUROC, this may be a trickier concept for people, who do not think about this all the time, to wrap their heads around. <br /><br />Again, thank you for taking the time to contribute your comments!Marya Zilberberghttps://www.blogger.com/profile/16080475886113209344noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-20860953701267709542010-12-16T21:59:18.909-05:002010-12-16T21:59:18.909-05:00Thank you for giving me the opportunity to clarify...Thank you for giving me the opportunity to clarify. And I apologize for the long post.<br /><br />The sensitivity and specificity values used in my calculations are based on a meta-analysis of 89 studies published recently in Annals of Internal Medicine by Schuetz et al, Ann Int. Med. 2010; 152:167-177. The sensitivity and specificity values apply to CT scanners with greater than 16 rows (typically 64-row detectors are common in clinical practice). But your point is right, the predictive accuracies depend upon the sensitivity and specificity of the diagnostic test.<br /> <br />With regards to pretest likelihood of CAD, it is modulated by the typicality of symptoms, age, gender and risk factors. For example, a 55 year old female with atypical chest pain will have a 10% likelihood of CAD without risk factors and 47% likelihood of CAD with risk factors. The probabilities increase to 45% and 79% for a 55 year old male with atypical symptoms. So even if the pretest likelihood is, say 20%, the PPV is 69% and NPV is 99% (I must clarify that my previously posted PPV and NPV values were based on a 50% prevalence of CAD).<br /><br />Another useful measure is the positive likelihood ratio (LR+) or negative likelihood ratio (LR-). The LR+ for CT angio is 8.9 and LR- is 0.02 (both consistent with large effects). Perhaps, the best metric for performance of a diagnostic test is area under the curve (AUC) which discriminates those with from those without disease. The AUC value of 0.98 for CT angio makes it a highly discriminant test. <br /><br />Hope this is useful.<br /><br />I must say that I find your posts very illuminating.<br />Thank youSanjay Kaulnoreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-42463337665589059772010-12-16T21:04:22.355-05:002010-12-16T21:04:22.355-05:00Dear Dr. Kaul,
It is an honor to have you visit a...Dear Dr. Kaul,<br /><br />It is an honor to have you visit and comment. While I cannot dispute your assertion that her risk for CAD is 30%, you do use the best possible test characteristics (sensitivity 98%, specificity 89%) to arrive at her posterior probability. If we use the most conservative estimates mentioned in the paper, along with a prior probability of 30% for CAD, we get the PPV of 49% and NPV of 96%. I can see how for some 50% may mean the need for further testing, while for others it may mean wait and see. <br /><br />But regardless of the particulars of the case, I think you and I both agree that this is an important exercise to engage in prior to ordering the test.<br /><br />Thank you again fro stopping by and commenting!Marya Zilberberghttps://www.blogger.com/profile/16080475886113209344noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-20192628387307144092010-12-16T20:33:53.832-05:002010-12-16T20:33:53.832-05:00It seems to me that the authors of the Archives ca...It seems to me that the authors of the Archives case report have conflated likelihood of obstructive coronary artery disease (CAD) with Framingham risk score-derived risk of coronary death or nonfatal heart attack events.<br /><br />While they are correct in stating that the risk of coronary death or nonfatal heart attack over 10 yrs is less than 10% (thereby implying low risk), a 52 year-old obese female with high blood pressure and ATYPICAL CHEST PAIN has an INTERMEDIATE (about 30%) likelihood of having obstructive CAD. A CT angiogram would be quite reasonable in this patient provided coronary artery calcium (CAC) score is less than 400. No mention is made of CAC score in the case report but the main coronary artery (LAD) had a complex calcified lesion that precluded evaluation of coronary stenosis. Even if the CT angiogram was accurate in diagnosing LAD stenosis, how would one have prevented a rare, but known, complication of invasive angiography? I think both the authors' and the editorialists' comments are right on target, but for the wrong reason.<br /><br />I think CT angiogram (sensitivity of 98% and specificity of 89%) is quite reasonable for someone with intermediate likelihood of CAD (pretest likelihood of 30%). The PPV of 90% and NPV of 98% of the test means that a positive test would increase the pretest probability from 30% to about 80% and a negative test would reduce the probability to under 3%. Reverend Bayes would regard such a test to have clinically relevant diagnostic yield!Sanjay Kaulnoreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-10597005621935660452010-12-16T20:08:09.205-05:002010-12-16T20:08:09.205-05:00Chuk, thanks for taking the time to comment! Agree...Chuk, thanks for taking the time to comment! Agree that cost is not the winning argument here -- it is quite simply the risk-benefit equation, given the patient's profile. <br />Mitzi, I could not agree more. When we talk about science literacy and numeracy, schools should be the place to assure this kind of basic preparation. Yet, we are lagging so badly behind the rest of the world. Sometimes I lose hope that we can actually empower people to be better users of the system. But I will keep on with my message! Thanks for the encouragement.Marya Zilberberghttps://www.blogger.com/profile/16080475886113209344noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-40606340089147034172010-12-16T19:59:58.270-05:002010-12-16T19:59:58.270-05:00I think basic statistics should be a requirement f...I think basic statistics should be a requirement for high school graduation in this country, and informed consent should involve an honest review of the stats. Would the woman have had the procedure done if she truly knew the risks down the road? What if she had a connective tissue disorder (as I do- it is found in 1/2000 people, approximately, and grossly under-diagnosed in women) that could make vascular complications more likely? I think the patient, once stabilized and calmed, should be offered multiple options of varying invasiveness and cost, if possible, with the stats for success/harm for each, and equipped to make a rational decision with the doctor. As it is, he/she is often pressured by lawsuit-wary doctors to take invasive tests with the benefits of subsequent (expensive, marginally useful) treatment emphasized and harms minimized. The doctor walks with the cash, and the patient and his/her primary physician live (or not) with the consequences. Most docs mean well, but I've encountered several that did not. Please spread the idea that the stats are important as far as you can. I've stared a physician down with papers in hand more than once now, and being perceived as a nut is getting old (You don't want a mammogram in your 30s? You like physical therapy better than surgery? Crazy.). Thanks.mitzihttps://www.blogger.com/profile/04492882647541112728noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-84974533955632033452010-12-16T18:38:55.528-05:002010-12-16T18:38:55.528-05:00Excellent job Marya. This is the kind of discussi...Excellent job Marya. This is the kind of discussion I used to have with residents. In many cases I would become dismayed when instead of a robust discussion of the relative merits of basing clinical discussions on probabilities my residents would essentially invoke the "more is better" argument or the "well you never can be sure" argument or the "what if it were your wife" argument as reasons to pursue additional diagnostic tests or invasive procedures which are implicitly assumed to be risk-free.<br /><br />This (in my opinion) is the real problem. People do not even allow themselves to see a Bayesian argument because the default position in Medicine is that intervention trumps non-intervention. <br /><br />Even before a discussion of statistics I always told my residents that it's better to as "why" rather than "why not". The former seeks information. The latter seeks an excuse to act.<br /><br />With regard to Dr. Synonymous' point about cost I would say that adding cost to the mix can actually get us to worse outcomes than a strictly statistical approach. <br /><br />Quite simply; in a construct that emphasizes cost those with means will be more likely to pursue an intervention/test/procedure while those without will (on average) be less likely to consider the same intervention/test/procedure. This, then, introduces incentives to either perform or not perform the intervention/test/procedure that are not (by definition) clinical. <br /><br />Unfortunately (or fortunately) health related expenditures do not follow a free-market consumer oriented algorithm.Anonymoushttps://www.blogger.com/profile/00667453506848186515noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-86166894945429369122010-12-16T12:04:42.239-05:002010-12-16T12:04:42.239-05:00Well, Dr. Jenner, great to see you back! Thanks fo...Well, Dr. Jenner, great to see you back! Thanks for your comment. Unfortunately, the idea of studying these new technologies and their findings at the population level collides with our view of the ethical considerations Take MRI for breast cancer detection. Do all the cancers they detect go on to cause problems? It is clear from Gil Welch's work that they do not, at least not all. But how do you design a study where you merely monitor some of the women over time once they know they have a cancer?<br />Until our discussion of ethics gets back to weighing all of the risks and benefits, rather that simply straying into the emotional quicksands of "cancer", we will not get a better sense of prior probabilities.Marya Zilberberghttps://www.blogger.com/profile/16080475886113209344noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-40442457318240839632010-12-15T18:46:03.615-05:002010-12-15T18:46:03.615-05:00Bayes is the way of the future. This sort of wari...Bayes is the way of the future. This sort of wariness of investigating too far should be a natural impulse of a good clinician. Antenatal ultrasounds and new higher-Tesla MRI scanners are examples of new technologies which currently provide results which provide temptation to investigate further but which we know little about the significance of. Renal pelvis dilatation detected antenatally may mean some risk of vesicouereteric reflux, renal scarring and renal failure but we have little idea how much risk (the modest knowledge we already have relates to children who have actually had a UTI, not just abnormal ultrasound appearance). Higher resolution scans lead to more bubs referred with findings. Similarly neurologists tell me they're seeing more findings on MRI brains these days that are hard to provide advice about and simply would not have been seen with CT or earlier MR technology (and don't whatever you do send these patients to a neurosurgeon, they will reach for the biopsy gun faster than you can say 'informed consent). We can't yet analyse these sorts of cases with Bayesian methods but that should be the aim of research- prospective series with outcomes, providing likelihood ratios we can get our teeth into. And not a p-value in sight.<br /><br />@ Dr Syn, agree entirely, but would also like to add that patients should also be part of the decision-making, not only the physician-steward. There are economic systems of health care delivery which would give patients more power (and responsibility) about spending decisions; such systems are not supported by either political side of the healthcare debate in your country, or in mine for that matter).Anonymousnoreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-83998170790599184452010-12-15T11:03:10.857-05:002010-12-15T11:03:10.857-05:00Thanks, Pat. I am not sure that cost would have de...Thanks, Pat. I am not sure that cost would have definitely avoided the cascade that ensued -- perhaps in some cases, but not in others. My point is that even without invoking cost, that third rail of the healthcare debate, we can make some solid clinical arguments for the "less is more" philosophy. It also argues for slow medicine, since the clinician needs to have time to actually think about the patient.<br />Thanks again for your comment!Marya Zilberberghttps://www.blogger.com/profile/16080475886113209344noreply@blogger.comtag:blogger.com,1999:blog-4519234397783312626.post-20139596952093732492010-12-15T10:53:06.410-05:002010-12-15T10:53:06.410-05:00Great Post and incredibly valuable to decision mak...Great Post and incredibly valuable to decision makers.<br />In the case mentioned, cost might be the main decision factor that would have avoided the disaster. The persons involved seem to assume FREE as the price of the test. If the patient was also a Consumer during a brief moment with the physician, who should be aware of their professional added role of Steward of scarce, valuable resources, the no scan decision might have been made in less than Bayesian mode. Just a thought, but your posts are awesome. Thanks!A. Patrick Jonas, MDhttps://www.blogger.com/profile/15935504320560038973noreply@blogger.com