Use of CTPA in Diagnosis of Pulmonary Embolism

In 1998, the multidetector row computed tomographic pulmonary angiography (CTPA) was introduced, changing the way physicians approach pulmonary embolism (PE). The test was expected to improve outcomes of PE by detecting and allowing treatment of emboli that had been overlooked with earlier tests, including ventilation-perfusion scans and invasive pulmonary angiography. In the Medicare fee-for-service population, there was an 11-fold rise in chest computed tomographic angiography from 2001 to 2006; in 2007 there were 2.6 million performed in the United States. CTPA is now recommended as the first-line test for PE by professional societies and practicing clinicians. However, according to researchers, there may be a downside to the increased sensitivity of CTPA: the test is able to detect emboli that are so small, they are clinically insignificant; this has been referred to as overdiagnosis, defined as the detection of an abnormality that will never cause symptoms or death. Overdiagnosis can lead to overtreatment, exposing patients to possible adverse events related to unnecessary treatment. The researchers recently conducted an investigation to determine whether CTPA has resulted in overdiagnosis in the United States. They reported results of their investigation in Archives of Internal Medicine [2011;171(9):831-837]. Using the Nationwide Inpatient Sample and Multiple Cause-of-Death databases, the researchers conducted a time trend analysis to assess the impact of CTPA on national PE incidence, mortality, and treatment complications. Because there was no direct way to prove that a PE has been overdiagnosed, the researchers looked for indirect evidence by comparing trends in PE incidence and mortality before and after the introduction of CTPA. They said that if CTPA was improving the ability to find and successfully treat clinically important pulmonary emboli, there would be an expected increase in incidence and a reduction in mortality. However, if CTPA primarily improves the ability to find pulmonary emboli of minimal clinical significance, the expectation would be rising incidence, but little change in mortality. They compared age-adjusted incidence, mortality, and treatment complications, including in-hospital gastrointestinal tract or intracranial hemorrhage of secondary thrombocytopenia, among adults in the United States from 1993 to 1998 (before introduction of CTPA) and from 1998 to 2006 (following introduction of CTPA). In the study period before CTPA introduction, overall age-adjusted incidence of PE did not change significantly; in the period following CTPA introduction, the incidence increased by 81%, rising from 62.3 to 112.3 per 100,000 US adults (P<.001). In a subset of patients with a primary diagnosis of PE, incidence rose 19% before CTPA introduction compared with a rise in incidence of 72% following introduction of CTPA (from 38.3 to 65.8 per 1000; P<.001). The age-adjusted PE case fatality improved slightly prior to introduction of CTPA (8% decrease, from 13.2% to 12.5%; P=.02) and substantially after CTPA introduction (36% decrease, from 12.1% to 7.8%; P<.001). Prior to the introduction of CTPA, the annual percentage change (APC) in case fatality among patients with PE was similar to that among all medical admissions; following the introduction of CTPA, case fatality decreased by a third for all patients with PE and by half for patients with a primary diagnosis of PE, while falling only 20% among all medical admissions. Finally, the introduction of CTPA was associated with an increase in presumed in-hospital complications of anticoagulation for PE. Prior to CTPA, the age-adjusted complications incidence rate did not change significantly; following CTPA introduction, the rate increased by 71% from 3.1 to 5.3 per 100,000 (APC, 7/0%; P<.001). In summary, the researchers said that, “the introduction of CTPA was associated with changes consistent with overdiagnosis: rising incidence, minimal change in mortality, and lower case fatality. Better technology allows us to diagnose more emboli, but to minimize harms of overdiagnosis we must learn which ones matter.”