USPSTF Stays Neutral on Global ABI Testing in Asymptomatic PAD

Marlene Busko

July 12, 2018

There is still not enough evidence to recommend for or against using the ankle-brachial index (ABI) test to screen for peripheral arterial disease (PAD) in adults without symptoms, such as claudication in the lower leg, a US Preventive Services Task Force (USPSTF) report concludes.

In a statement and evidence summary published July 10 in JAMA, the USPSTF arrived at the same conclusion as in their 2013 report — insufficient evidence.  

"In asymptomatic folks we did not find evidence that the benefits of screening [with ABI] outweighed any potential harms," task force member C. Seth Landefeld, MD, from the University of Alabama at Birmingham, summarized to theheart.org | Medscape Cardiology.

"It doesn't mean that [such screening isn't warranted]; it's just that we didn't find compelling evidence" for it.

Instead, clinicians should "focus on evaluating cardiovascular risk with well-established tools such as the Pooled Cohort Equations," he said, "and then implement previously recommended interventions, such as blood pressure control, smoking cessation, or preventive statins or aspirin. These things do have very definite benefits." 

"I want to emphasize that this is not a recommendation against screening for PAD; it's a recommendation that there's insufficient evidence for across-the-board screening," echoed Mary M. McDermott, MD, from Northwestern University Feinberg School of Medicine, Chicago, Illinois, who cowrote an editorial about the statement.

"Screening specifically applies to people who don't have leg symptoms," she stressed in an interview with theheart.org | Medscape Cardiology. But "most people with PAD have leg symptoms if you look carefully."

"PAD is common and it's often unrecognized, undiagnosed, and undertreated," she said. "But a lot of that has to do with the fact that we don't ask patients carefully enough about leg symptoms that may indicate PAD."

Patients who have leg symptoms "should all be tested with ABI," she noted.

Five New Studies, No Strong Evidence

PAD, which is a manifestation of systemic atherosclerotic disease, not only can impair walking ability but also lead to infection and amputation in severe cases, USPSTF chair Susan J. Curry, PhD, from the University of Iowa in Iowa City, and colleagues note.

Because a low ABI is associated with an increased risk for cardiovascular disease (CVD) events, screening asymptomatic adults for PAD with the ABI might reduce morbidity or mortality from PAD or CVD.

To update its 2013 report, the task force identified five studies published between 2012 and 2017 that screened for PAD in a total of 5864 asymptomatic participants with no known cardiovascular disease.

One study, which compared the diagnostic accuracy of ABI vs the gold standard, MRI, found that ABI had low sensitivity (7% to 34%) and high specificity (96% to 100%).

Regarding the question of whether treatment of screen-detected ABI leads to improved health outcomes in asymptomatic adults, two trials —  AAA and POPADAD — both in patients with and without diabetes and low ABI (≤0.95 or ≤0.99), found no significant effect of aspirin for composite CVD outcomes.

In addition, two supervised-exercise studies found no significant improvement in walking ability in asymptomatic patients.

No studies directly addressed the harms of screening for PAD with the ABI, although the potential exists for "false-positive test results (about 1%), false-negative test results (80% to 85%), exposure to gadolinium or contrast dye from confirmatory MRA [magnetic resonance angiography] or CT angiography, anxiety, labeling, and opportunity costs," the authors caution.

Further, "The time and resources needed to screen with the ABI in a primary care setting may detract from other prevention activities that may have more benefit." Thus, they were not able to recommend for or against screening.

ABI in Borderline Risk  

Finding a patient with a low ABI with no other traditional cardiovascular risk factors is very rare, Landefeld noted. 

During a 25-year follow-up of healthy, 40- to 75-year-old US men free of CVD, there were only 9 PAD cases/100,000 men per year among those with none of four traditional cardiovascular risk factors: current smoking, hypertension, high cholesterol, or type 2 diabetes.

The four risk factors accounted for 75% of PAD cases, and 96% of men diagnosed with PAD had at least one of these risk factors.

Thus, a patient with unknown PAD would already be identified as having an increased cardiovascular risk based on a traditional screening tool, such as the Pooled Cohort Equations.

"Among people without symptoms of claudication or other symptoms equivalent to that, focusing on evaluating their cardiovascular risk with well-established tools such as the Pooled Cohort Equations and treating them accordingly is something that we definitely recommend strongly," said Landefeld

The USPSTF has specific recommendations, he noted, for screening for hypertension and diabetes; statin use; and counseling on smoking cessation, healthy diet, and physical activity. 

In certain cases, clinicians "may want to perform the ABI in the asymptomatic patient if their risk is borderline," suggested McDermott.

For example, the American Heart Association/American College of Cardiology recommends prescribing a statin if the patient has at least a 7.5% risk for a cardiovascular event in the next 10 years. "So if someone has a risk of 6% or 8% but they are reluctant to take a statin, then knowing that they have a low ABI would be a definite reason that they should be on a statin," she said.

The US Congress mandates that the Agency for Healthcare Research and Quality support the operations of the USPSTF, an independent voluntary body. Members of the USPSTF received travel reimbursement and honorarium for participating in USPSTF meetings. McDermott reported receiving grant support from the National Heart, Lung, and Blood Institute, National Institute on Aging, Novartis, Regeneron, and the Patient-Centered Outcomes Research Institute and receiving supplied therapy for clinical trials from Hershey’s, Reserveage, and ViroMed. Editorial coauthor Michael Criqui reported no disclosures.

JAMA. Published July 10, 2018. Evidence reportRecommendation statement, Editorial

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