Compression sonography in patients with indeterminate or low- probability lung scans: lack of usefulness in the absence of both symptoms of deep-vein thrombosis and thromboembolic risk factors

We sought to determine whether compression sonography could be eliminated in the evaluation of patients who lacked both thromboembolic risk factors and symptoms of deep-vein thrombosis and who had an indeterminate or low-probability lung scan. The medical records of 155 consecutive patients who underwent bilateral lower-extremity sonography after an indeterminate or low-probability lung scan were reviewed. The presence of thromboembolic risk factors and deep-vein thrombosis symptoms and the result of sonography were recorded. Patients were divided into two groups: group 1 consisted of patients with either thromboembolic risk factors or deep-vein thrombosis symptoms, and group 2 consisted of patients without thromboembolic risk factors and without deep-vein thrombosis symptoms. The incidences of deep-vein thrombosis in groups 1 and 2 were compared by use of a two-tailed Fisher's exact test. Thromboembolic risk factors or deep-vein thrombosis symptoms were found in 109 of 155 patients (70%) (group 1). Deep-vein thrombosis was found in nine of 108 patients (8%) in group 1. Both thromboembolic risk factors and deep-vein thrombosis symptoms were absent in 47 of 155 patients (30%) (group 2). Deep-vein thrombosis was found in none of 47 patients (95% confidence interval, 0-8%) in group 2. The difference in the incidences of deep-vein thrombosis in groups 1 and 2 approached statistical significance (p = .0579). The negative predictive value of the absence of both thromboembolic risk factors and deep-vein thrombosis symptoms in excluding deep-vein thrombosis was 100% (95% confidence interval, 93-100%). If both symptoms of deep-vein thrombosis and thromboembolic risk factors are absent, the usefulness of lower-extremity sonography in detecting deep-vein thrombosis in patients with an indeterminate or low-probability lung scan is low. The manner in which these findings may be used to modify individual practice patterns will undoubtedly depend on the rate of detection of deep-vein thrombosis at a given institution.