July 11, 2018
3 min read

USPSTF: Insufficient evidence regarding benefits, harms of ankle-brachial index for PAD, CVD risk

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Mary McDermott
Mary M. McDermott

The U.S. Preventive Services Task Force has given a class I indication for the use of ankle-brachial index to screen patients who are asymptomatic for peripheral artery disease and CVD risk due to insufficient evidence that assessed the benefits and harms of this screening method, according to a recommendation statement published in JAMA.

The USPSTF released a draft recommendation statement in January, which gave the same indication for ankle-brachial index (ABI).

“To update its 2013 recommendation, the USPSTF reviewed the evidence on whether screening for PAD with the ABI in generally asymptomatic adults reduces morbidity and mortality from PAD or CVD,” the task force wrote in the recommendation statement. “The current review expanded on the previous review to include persons with diabetes and interventions that include supervised exercise and physical therapy intended to improve outcomes in the lower limbs.”

Prevalence of low ABI

Although it has been estimated that 5.9% of the U.S. population aged 40 years or older have a low ABI, the true prevalence of the condition is difficult to estimate because patients with a low ABI often have atypical symptoms or are asymptomatic, according to the recommendation statement.

There is inadequate evidence that shows that ABI is accurate when identifying patients who are asymptomatic with PAD and those who can benefit from treatment. In addition, there is also inadequate evidence showing the clinical benefit in screening for and treating patients who are asymptomatic with PAD.

Adequate evidence has been found that the direct harms of screening are minimal. Harms associated with screening include exposure to gadolinium or contrast dye, false-positive test results, labeling, anxiety and opportunity costs. Further evaluation for CVD as a result of a low ABI finding can also lead to the harms associated with angiography and stress testing. Preventive treatment for CVD or PAD is also associated with harms such as diabetes for those treated with statins and bleeding for patients treated with aspirin.

“The USPSTF concludes that the current evidence is insufficient to assess the balance of benefits and harms of screening for PAD and CVD risk with the ABI in asymptomatic adults,” the task force wrote.

In patients who are asymptomatic without a known diagnosis of CVD, PAD or severe chronic kidney disease, clinicians should consider several factors when deciding whether to screen for PAD with ABI: potential preventable burden, potential harms and current practice.

Although resting ABI is the most commonly used measurement to diagnose PAD, variations in measurement protocols may result in differences in ABI values. Physical examination in patients who are asymptomatic has been shown to have low sensitivity, although the clinical benefits and harms for this method have not been well-evaluated, according to the recommendation statement.

Focus on treatment

PAD treatments focus on preventing CVD events from systemic atherosclerosis and reducing morbidity and mortality from lower limb ischemia. Interventions to prevent CVD events include lowering cholesterol levels, smoking cessation, managing high BP and antiplatelet therapy.

Future research should focus on whether screening for PAD with ABI improves clinical outcomes, in addition to the patient population that may have an increased risk for PAD who are not already being treated to reduce CV risk. Further studies should also include screening with ABI and intervention to halt disease progression in the lower limbs in groups such as racial/ethnic minorities, women or those with a lower socioeconomic status, as well as those at high risk, including patients with diabetes.

“The USPSTF recognizes these well-established disparities in care,” the task force wrote in the recommendation statement. “However, the evidence on screening and treatment in these groups is currently lacking, and the USPSTF was unable to determine the overall balance of benefits and harms. Future research should include diverse populations and report on their outcomes.”

Michael H. Criqui

In a related editorial, Mary M. McDermott, MD, Jeremiah Stamler Professor and professor of medicine and preventive medicine at Northwestern University Feinberg School of Medicine, and Michael H. Criqui, MD, MPH, professor in the department of family medicine and public health at University of California San Diego, wrote: “The conclusions of the USPSTF should not be misconstrued as a determination that PAD is not common, clinically important or associated with significant adverse outcomes. Further research is needed to identify therapies that improve functional performance and prevent cardiovascular events in asymptomatic people with an ABI less than 0.9, which could provide sufficient evidence to support ABI screening in asymptomatic people. Until then, a careful history to identify ischemic leg symptoms in older people is likely to significantly improve PAD detection and treatment.” – by Darlene Dobkowski

Disclosures: The task force members and Criqui report no relevant financial disclosures. McDermott reports she received grant support from NHLBI, National Institute on Aging, Novartis, Regeneron and the Patient-Centered Outcomes Research Institute, and received supplied therapy for clinical trials from Hershey’s, Reserveage and Viro.