Noninvasive venous examinations as a screening test for pulmonary embolism

Blood clots that cause pulmonary embolism are reputed to arise in the lower extremities in 95% of cases and, therefore, testing with noninvasive venous studies has been recommended as a screening method. We evaluated plethysmography results and Doppler venous flow sounds for their concordance with pulmonary angiograms in a group of patients with suspected pulmonary embolism, and for their concordance with venograms in a second group of patients with suspected deep venous thrombosis. Fifty patients had both pulmonary angiograms and noninvasive venous studies. Of 16 patients with positive noninvasive studies, ten had angiograms positive for pulmonary embolism, and six had negative angiograms. Of 34 patients with negative noninvasive studies, 16 had positive pulmonary angiograms and 18 had negative angiograms. The positive predictive value was 63% and the negative predictive value was 53%. By contrast, in 125 patients with suspected deep venous thrombosis, the positive and negative predictive values of noninvasive studies were 94% and 92%, respectively. In this retrospective study, positive noninvasive examinations were useful clinically, but noninvasive venous studies were frequently negative in patients with documented pulmonary embolism and cannot be used to exclude this diagnosis.