'Insufficient Evidence' for ABI Screening in Silent PAD: USPSTF Statement

Marlene Busko

September 03, 2013

ROCKVILLE, MARYLAND The US Preventive Services Task Force (USPSTF) examined the value of using the ankle-brachial-index (ABI) test to detect peripheral arterial disease (PAD) and predict the risk of CVD in patients without PAD symptoms, CVD, severe chronic kidney disease, or diabetes [1]. The verdict? It issued an "I statement," meaning that there is "insufficient evidence" to recommend using or not using the screening test in this patient population.

In a 2005 statement, the USPSTF had advised against routine screening to detect PAD in primary care (a D recommendation). However, the new statement has a broader focus. The task force looked at two questions: Will this screening add prognostic value beyond that obtained from a Framingham risk score, and would these patients be treated differently and have less risk of CVD events?

"Sometimes it's challenging to communicate what 'insufficient' is," task force member Dr Kirsten Bibbins-Domingo (University of California, San Francisco," told heartwire . "It doesn’t mean that we are recommending for or against" using the ABI test.

The "I statement" was issued because although it found that "low ABIs are [clearly] associated with [CVD] risk . . . the amount that they contribute above and beyond Framingham risk for correctly classifying [risk in] people may be only small, based on existing evidence," she continued. "When treatments [were] initiated based on the ABIs from screening, there was no evidence of additional benefit."

The statement does not apply to people who already have symptoms such as leg pain when walking that is relieved by rest, she stressed. "We are not talking here about screening people who already have symptoms, who should certainly be evaluated, and we're not talking about people with CVD or diabetes, who should be treated in accordance with all of the things that we know work," she cautioned.

The evidence review by Dr Jennifer S Lin (Kaiser Permanente Northwest, Portland, OR) and colleagues [2] and the recommendation by task force chair Dr Virginia A Moyer (American Board of Pediatrics, Chapel Hill, NC) and colleagues are published September 3, 2013 in the Annals of Internal Medicine.

Review Finds Unclear Evidence

It is important to investigate the value of the ABI screening test, because the prevalence of PAD is increasing, Moyer and colleagues write. Patients with PAD not only have potential leg pain, they are at heightened risk of MI or stroke. ABI is a noninvasive test, which could be done in a primary-care physician's office, although it is usually done by a vascular surgeon, Bibbins-Domingo said.

According to the task force report, 5.9% of US adults have a low ABI (typically <0.9), which is considered a surrogate for PAD. The prevalence of PAD increases from 1.9% of 40- to 59-year-olds to 8.1% of 60- to 74-year-olds to 17.5% of adults age 75 and older.

Lin and colleagues searched the literature for studies in English published from 1996 to 2012 and identified 15 fair- to good-quality studies that looked at the predictive value of ABI and two studies that looked at treatment benefits and harms from ABI.

They found inadequate evidence that ABI test results provided additional information to predict CVD risk, beyond the Framingham risk score. One study showed that initiating low-dose aspirin treatment in asymptomatic patients with low body-mass index (BMI) might increase the risk of bleeding.

According to Bibbins-Domingo, "fortunately, there are many things that we know work . . . to modify a patient's cardiovascular disease risk," such as eating a healthy diet, maintaining a healthy weight, exercising regularly, and not smoking.

Further research is needed to identify potential high-risk subgroups, such as older patients with atypical symptoms, who might benefit from ABI screening, she added.

"Definitive Randomized, Controlled Trial Needed"

In an accompanying editorial [3], Dr Mary McGrae McDermott (Northwestern University, Chicago, IL) writes that the task force's conclusion "may seem surprising" at first. Since patients with PAD often present with no or atypical symptoms and could be diagnosed noninvasively by ABI in a clinician's office, the test might be expected to reduce cardiovascular morbidity and mortality.

However, the findings are partly explained by the observation that ABI may not add any meaningful information beyond the Framingham risk score, she notes.

Given the growing number of people with PAD, there is an urgent need for a randomized controlled trial of ABI screening, according to McDermott. "Establishing whether ABI screening improves outcomes is a global imperative for the growing number of persons with undiagnosed PAD," she writes. "A definitive randomized, controlled trial is needed to determine whether ABI screening improves health outcomes in persons at risk for PAD."

The review by Lin and colleagues was conducted by the Kaiser Permanente Research Affiliates Evidence-based Practice Center under contract to the Agency for Healthcare Research and Quality (AHRQ). Moyer reports receiving support for travel to meetings from the AHRQ. Lin reports no conflicts of interest. McGrae McDermott reports grants to her institution from the National Institutes of Health; having consulted for Ironwood Pharmaceuticals; support for travel to meetings from the American Heart Association; fees for participation in review activities such as data monitoring boards, statistical analysis, and end-point committees from the University of Florida Pepper Center; and being the medical editor for peripheral artery disease for the Foundation for Informed Medical Decision Making. Disclosures for the coauthors are listed at https://annals.org .


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