AJR: Self-referral strikes again? Study questions carotid U.S. exams

Intervention in asymptomatic carotid artery stenosis is controversial and screening for carotid artery stenosis has received a “D” grade from the U.S. Preventive Services Task Force. Despite the questionable evidence supporting the procedure, an increasing number of Medicare beneficiaries are being screened with carotid duplex ultrasound, possibly driven by self-referrals from specialists performing revascularization, according to a study published in the April issue of the American Journal of Roentgenology.

Abdul Mueed Zafar, MD, of Rhode Island Hospital in Providence, and colleagues noted that carotid duplex ultrasound is performed in more than 90 percent of asymptomatic individuals before a carotid intervention, such as carotid endarterectomy or carotid artery stenting. Because providers offering revascularization procedures also often offer carotid duplex ultrasound, there are “potentially enhanced economic incentives for diagnostic testing by vascular specialists in a position to self-refer for both of these services.”

To test the hypothesis that providers of revascularization are incentivized to increase the number of carotid duplex ultrasound exams, the authors analyzed ultrasound screening utilization among Medicare beneficiaries between the years 2000 and 2007. Rates of carotid duplex ultrasound were compared among three specialties that perform revascularization for carotid stenosis—interventional radiology, vascular surgery and cardiology—and diagnostic radiology, which usually does not.

More than 11 million procedures were performed by the four specialties during the study period, and utilization increased for all, though at different rates.

When broken down by specialty, the results supported the author’s hypothesis as carotid duplex ultrasound rates grew much more slowly in diagnostic radiology compared with the other specialties. Utilization by diagnostic radiology increased at a compound annual growth rate of 1 percent during the study period, whereas interventional radiology and vascular surgery saw compound annual growth rates of 3 and 6 percent, respectively. Utilization by cardiology increased by a compound annual growth rate of 11 percent, the highest of all, with an additional 960 procedures per 100,000 Medicare beneficiaries in 2007 compared with 2000.

“Symptom rates or disease prevalence in the population are unlikely to be subject to enough year-to-year variation to account for substantial changes in utilization,” wrote the authors. “It is more likely that the prevalence of disease in the population varies little from year to year and that differences in utilization are attributable to differences in practice patterns.”

The authors noted that while the growth in carotid duplex scans by specialties that provide carotid interventions is noteworthy, the dataset they used did not track referral patterns, so definitive descriptions of overutilization by certain specialties can’t be made.

“Because the disease’s prevalence in the Medicare population is low (approximately 1 percent), the specificity of carotid duplex ultrasound is not high (approximately 87 percent), and the treatment effect size compared with medical management is small, such a strategy may lead to unnecessary procedures and, population wide, cause more strokes than it prevents,” concluded Zafar et al.