Subsequent pulmonary embolism: Risk after a negative helical CT pulmonary angiogram - Prospective comparison with scintigraphy

PURPOSE: To determine whether a helical computed tomographic (CT) scan that is negative for pulmonary embolism (PE) is a sufficiently reliable criteri on to safety withhold anticoagulation therapy. MATERIALS AND METHODS: Patients with negative helical CT scans were prospec tively compared with patients with negative or low-probability scintigrams. In a 460-bed university hospital and clinic, 1,015 adult patients underwen t either scintigraphy or helical CT for possible PE for 25 months. Five hun dred forty-eight patients who had negative images and were not receiving an ticoagulation therapy were prospectively followed up for 3 months for clini cal, new imaging, death certificate, or autopsy evidence of subsequent PE. Ninety-seven patients were lost to follow-up. RESULTS: Subsequent PE was found in two (1.0%) of 198 patients with negativ e CI scans, none of 188 patients with negative ventilation-perfusion (V-P) scans, and five (3.1%) of 162 patients with low-probability V-P scans (not statistically significant). Patients in the helical CT group were hospitali zed more often, had more severe disease, had more substantial PE risk facto rs, and had a higher death rate. No deaths were attributed to PE in either group. CONCLUSION: The frequency of clinical diagnoses of PE after a negative CT s can was low and similar to that after a negative or low-probability V-P sca n. Helical CT is a reliable imaging tool for excluding clinically important PE.