Finding an alternative diagnosis does not justify increased use of CT-pulmonary angiography

Background: The increased use of computed tomography pulmonary angiography (CTPA) is often justified by finding alternative diagnoses explaining patients' symptoms. However, this has not been rigorously examined. Methods: We retrospectively reviewed CTPA done at our center over an eleven year period (2000 - 2010) in patients with suspected pulmonary embolus (PE). We then reviewed in detail the medical records of a representative sample of patients in three index years - 2000, 2005 and 2008. We determined whether CTPA revealed pulmonary pathology other than PE that was not readily identifiable from the patient's history, physical examination and prior chest X-ray. We also assessed whether the use of pre-test probability guided diagnostic strategy for PE. Results: A total of 12,640 CTPA were performed at our center from year 2000 to 2010. The number of CTPA performed increased from 84 in 2000 to 2287 in 2010, a 27 fold increase. Only 7.6 percent of all CTPA and 3.2 percent of avoidable CTPAs (low or intermediate pre-test probability and negative D-dimer) revealed previously unknown findings of any clinical significance. When we compared 2008 to 2000 and 2005, more CTPAs were performed in younger patients (mean age (years) for 2000: 67, 2005: 63, and 2008: 60, (p=0.004, one-way ANOVA)). Patients were less acutely ill with fewer risk factors for PE. Assessment of pre-test probability of PE and D-dimer measurement were rarely used to select appropriate patients for CTPA (pre-test probability of PE documented in chart (%total) in year 2000: 4.1%, 2005: 1.6%, 2008: 3.1%). Conclusions: Our data do not support the argument that increased CTPA use is justified by finding an alternative pulmonary pathology that could explain patients' symptoms. CTPA is being increasingly used as the first and only test for suspected PE.