Blood Clot Screening of Lungs Leads to ‘Overdiagnosis,’ Researchers Find

New screening technology that led to more blood clots being found in the lungs can’t always detect which ones may be fatal, causing some patients to undergo unnecessary treatment, researchers said.

The U.S. incidence rate for pulmonary embolism increased 81 percent during the first eight years after the high-resolution scanning was introduced in 1998. The mortality rate declined 3 percent over that period, suggesting more patients with non- life-threatening clots are being diagnosed, a team led by Renda Soylemez Wiener, a professor at the Boston University School of Medicine, reported today in the Archives of Internal Medicine.

The scans, called multidetector row computed tomographic pulmonary angiography, are detecting clots that don’t always need treatment, which has led to “overdiagnosis” and to patients being subjected to blood-thinning drugs like warfarin that won’t help and may be harmful, wrote Wiener and her colleagues. Medical-device makers including Fairfield, Connecticut-based General Electric Co. (GE) and Siemens AG (SIE) of Munich sell CT scanners.

“Rather than an epidemic of disease, we think the increased incidence of PE reflects an epidemic of diagnostic testing that has created overdiagnosis,” the authors wrote. “Much of the increased incidence in PE consists of cases that are clinically unimportant.”

Hospitals that spend as much as $2 million to purchase a CT scanner have a financial incentive to test as many patients as possible, which drives up costs for the U.S. health care system, said Shannon Brownlee, the acting director of health policy at the New America Foundation, a Washington-based research organization.

Expensive Machines

“These machines are very, very expensive so if you invest that much money in one of these things, you’re darn sure the hospital administrator wants lots of patients to be running through them to pay them off,” Brownlee said by telephone.

Spending by Medicare, the U.S. health program for the elderly and disabled, on medical imaging services including computed tomography scans rose 17 percent annually from 2000 to 2006, and overall imaging expenditures more than doubled to $14 billion a year, according to a 2008 report by the Government Accountability Office in Washington. The proportion of Medicare beneficiaries undergoing CT scans rose 39 percent during those years, the GAO reported.

The screenings are conducted with the same machines used at hospitals for other types of scans, Wiener said in a telephone interview. Prior to 1998, CT scanners lacked the resolution to detect blood clots in the lung, she said.

Finding More Clots

Researchers found that the incidence of pulmonary embolism increased to 112 cases per 100,000 U.S. adults between 1998 and 2006, compared with the rate in 1993 through 1998. The mortality rate associated with the ailment declined to 11.9 deaths per 100,000 U.S. adults during the later period.

The study is based on an analysis of data compiled by the National Center for Health Statistics, which is managed by the Atlanta-based Centers for Disease Control and Prevention.

Blood clots in lungs are typically treated with anticoagulants. Scans don’t always reveal whether the embolism has the potential to harm a patient, Wiener said. “It is currently our best test to diagnose PE and many PEs are clinically significant and do need to be treated,” she said. Doctors should “think more carefully” about when a test and treatments are necessary, she said.

To contact the reporter on this story: Jeffrey Young in Washington at jyoung89@bloomberg.net.

To contact the editor responsible for this story: Adriel Bettelheim at abettelheim@bloomberg.net.

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