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More overdiagnosis

Posted by medconsumers on May 17, 2011

Here is another disturbing example of a high-tech procedure finding abnormalities that are better left undetected. U.S. statistics show that the use of computed tomographic pulmonary angiography, a diagnostic test that uses contrast dyes and x-rays to see how blood flows through the lungs, has increased steadily since its introduction in 1998. This has led to a large increase in the detection of pulmonary embolism (PE), but only a minimal reduction in its death rate. Worse, this overdiagnosis of PE exposes more people to the considerable harms of unnecessary anticoagulant (blood-thinning) treatment.

“At first glance, the rapid increase in incidence seems alarming—an apparent epidemic of PE. But the epidemic is unusual because it has only occurred among nonfatal emboli… Moreover, an epidemic is unlikely without a corresponding increase in risk factors,” wrote Renda Soylemez Wiener, MD, and colleagues at the Dartmouth Medical School. “Rather than an epidemic of disease, we think the increased incidence of PE reflects an epidemic of diagnostic testing that has created overdiagnosis. In this scenario, much of the increased incidence in PE consists of cases that are clinically unimportant, cases that would not have been fatal even if left undiagnosed and untreated.”

In 2007, there were 2.6 million chest angiography scans performed in the U.S. Before this technology was introduced in 1998, the incidence of pulmonary embolism was unchanged. But PE diagnosis has since increased substantially, from 62 cases per 100,000 people to 112 cases per 100,000. During the same time period, there was only a slight decrease in mortality from 12.3 deaths to 11.9 deaths per 100,000. The rate of complications associated with anticoagulant treatment, such as brain hemorrhage and gastrointestinal bleeding, was also stable prior to the introduction of CTPA. It has since gone from 3.1 to 5.3 per 100,000.

Dr. Wiener, the lead author of this study, was asked how people can protect themselves from this form of overdiagnosis. “Right now I believe consumers are in a difficult situation,” she answered, explaining that doctors do not know which blood clots will become fatal if left untreated. “It is really up to doctors to think more carefully about reserving CT pulmonary angiography for situations in which there is a high pre-test probability of a pulmonary embolism based on symptoms, clinical presentation, etc.,” continued Dr. Wiener in a telephone interview. “We need a randomized controlled trial of treatment with anticoagulation versus close monitoring without anticoagulation to help sort out whether every small pulmonary embolism requires treatment.”

The study was published in Archives of Internal Medicine as part of this journal’s “Less is More” series, which addresses issues of overdiagnosis and overtreatment. Here’s one about CT scans and this about overtreatment of prostate cancer.

Maryann Napoli, Center for Medical Consumers©

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