Experts decry US Preventive Services Task Force recommendation against PAD screening

Dallas, TX - A Special Report in the August 22, 2006 issue of Circulation ^[1]] is calling on the United States Preventive Services Task Force (USPSTF) to revise its recommendation against screening for peripheral arterial disease (PAD) ^[2][3]. The USPSTF recommendations were written in 1996; a 2005 update made no changes to the "D" recommendation it gave to PAD screening—suggesting that it yields little or no benefit and potential harm.

Challenging that decision, Dr Joshua A Beckman (Brigham and Women's Hospital, Boston, MA) and colleagues state in their Circulation paper that the USPSTF recommendations are too narrow in focus and overlook the fact that the point of screening is not symptom improvement, but prevention of cardiovascular events.

"The USPSTF was against screening because of the low likelihood of reducing leg morbidity," Beckman explained to heart wire . "But screening typically means that you're looking for something in an asymptomatic population, so I don't really understand, when you're looking for patients without leg symptoms, how you're going to make their legs feel better," Beckman said. "What we are saying is that the real purpose of screening should be to prevent heart attack, stroke, and death."

But in defense of the recommendations, USPSTF chair Dr Ned Calonge (Agency for Healthcare Research and Quality, Rockville, MD) argues that it is unreasonable to fault the recommendations for not tackling the broader issue of CVD risk, when their stated aim is to assess whether screening would decrease PAD-specific morbidity.

"The task force recognized that people were using PAD screening as an adjunct to helping characterize CVD risk in other settings, but this review, which paralleled the initial recommendation, really asked, What's the evidence that screening for PAD in asymptomatic people improves outcomes in peripheral vascular disease? So, to me, the criticism seems awkward in that the task force's recommendations clearly state what it's for. . . . [It] wasn't intended to provide recommendations about the use of PAD screening for disease strategies in other systems."

In fact, Calonge told heart wire , the task force is currently conducting a review of multiple "novel risk factors" for CVD, PAD screening among them, that would form the basis of a separate USPSTF document that he hopes will be completed within the next year. While the topic of CVD risk came up in discussions of the PAD-screening update, it would not have been appropriate to mention a broader role for PAD screening, Calonge said. "We were stuck on that issue, because we had not done the review, so we couldn't really comment on something that might be useful if we hadn't even looked at it yet."

In their paper, Beckman et al outline, point by point, their concerns with the USPSTF and its failure to recognize "the most important unfavorable outcome faced by all individuals with PAD": namely, MI, stroke, and death. By contrast, they note, a recent ACC/AHA guideline for the management of PAD patients—coauthored or endorsed by all of the leading vascular disease societies and organizations, as well as the National Heart, Lung, and Blood Institute—recommends screening using the ankle-brachial index (ABI) so that therapeutic interventions can be initiated in patients with confirmed PAD. Moreover, the National Cholesterol Education Program has designated PAD a CHD risk equivalent, putting the risk of a PAD-associated ischemic event on par with the risk of a coronary event, warranting aggressive reduction in total and LDL cholesterol.

In fact, the USPSTF recommendations refer to other professional bodies that have disparate views on ABI testing and PAD screening, but nonspecialty groups tend to look for guidance from the USPSTF recommendations. According to Calonge, primary-practice physicians, family doctors, general internists, payers, and policy makers, make up the primary audience for USPSTF recommendations.

"Many people take their cues from the USPSTF," Beckman told heart wire , "For example, the Family Practice Society does not think it's worthwhile to do an ABI screening on the basis of that document. So as a result, we are missing the people who are asymptomatic, and that's the majority of the patients. Even though everyone who is a vascular specialist of some type agrees that these patients should be looked for, sought after, and treated, the doctors that would actually spend the most time trying to do this don't think it should be done because of the USPSTF."

To heart wire , Calonge acknowledged that a directive not to use PAD screening to screen for PAD will be largely interpreted as a directive not to screen for PAD at all—indeed, there is no sentence in the document that leaves a door open for PAD screening to have a role beyond that stated in the recommendations. But, Calonge insists, until such a role is proven, even hinting at this would have been misleading and inappropriate.

"That we haven't reviewed this yet or that the answer isn't in yet is something that clinicians are going to have to face," Calonge stated. "I can't anticipate the outcome of the review, but it may be still that the evidence isn't sufficient or that the study to prove what [Beckman et al] are promoting has not yet been completed. . . . Our job is to be the evidence-based stake in the sand. How advocates and other physicians deviate from the stake in the sand is clearly within their purview and medical judgment, but at least we can start with what the evidence supports."

Beckman et al are clear that they don't advocate blanket screening for PAD. On the basis of the ACC/AHA PAD guidelines, they call for screening of high-risk patients, defined as people under 50 with diabetes and one other atherosclerotic risk factor, people 50 to 69 with a history of smoking or diabetes, and all individuals 70 or older. And, they argue, the evidence base already supports targeted screening.

"I completely agree that a targeted screening process with implementation of treatment and [assessment of] long-term outcomes has not been done as a study, but each of the components has basically been done," Beckman told heart wire . "We know who has the disease from screening large populations; we know the drugs work from large randomized controlled trials; and we know that the outcomes are bad unless they're treated. You can be a purist, or you can actually realize that people are dying because they don't know they have this disease."

Beckman said that the primary goal of the Circulation special report was to raise awareness among physicians and perhaps catch the attention of regulators. "I would love to be able to get the federal government to pay for a one-time screening examination in the doctor's office. I'm not looking for it to do it every single time, although it's not even that much money."

It may be cheap, says Calonge, but he dismisses the idea that measuring ABI is appropriate use of time and money just yet, particularly when it is not yet clear what PAD screening adds over and above other risk-factor assessments. And until that's proven, he does not feel that the USPSTF document is causing physicians who follow its recommendations to overlook important diagnoses.

"If you could show me that we are preventing all the heart disease and prolonging all the lives we could with the things the task force already recommends, based on good evidence—screening and controlling cholesterol, blood pressure, and diabetes—I might feel differently that this recommendation is having a significant negative impact," Calonge stated. "But what I would like to see first is to implement the things that we know work, do those well, and we'll save lots of lives."

It's a stance that Beckman believes exemplifies the widespread misunderstanding of PAD.

"Classic CHD risk factors are just that: risk factors for disease, whereas PAD is the disease. It's the difference between the development of the problem vs having the problem," he explains. With ABI, Beckman continues, "you're not just trying to look for a risk for atherosclerosis, you are making the diagnosis of atherosclerosis." Many studies, he adds, have established the graded relationship between low ABI reflecting atherosclerosis in the legs and frequency of cardiovascular events.

For this reason alone, Beckman says PAD screening doesn't belong in a USPSTF review of "novel risk factors," nor should better management of known risk factors deflect attention from the need to identify people with PAD. "When you find someone who has significant PAD, even with the most recent data, their seven-year mortality rates are 25%." And screening studies suggest that between 10% and 20% of the Medicare population has PAD.

"My question is, Why would you ignore disease?" Beckman asks. "Not risk factors, disease. These patients don't have time to wait; they die now."

Heartwire from Medscape © 2006 

Cite this: Experts decry US Preventive Services Task Force recommendation against PAD screening - Medscape - Aug 25, 2006.