Purpose: This study tests the hypothesis that the absence of deep venous thrombosis (DVT) on lower extremity color-flow venous duplex examination (LECFD) combined with a non-high-probability ventilation/perfusion (V/Q) scanning results rules out pulmonary embolus (PE). The use of LECFD as a diagnostic aid for PE is based on data that show that 90% of PE originate from lower extremity DVT, and therefore on the assumption that PE cannot be present if DVT is not present as the source.
Methods: Over a 3-year period 51 patients with clinically suspected PE underwent LECFD and pulmonary angiography (PA) within 72 hours of each other. Forty-one patients also underwent V/Q scanning during the same time period. The results of LECFD and V/Q scans were compared with the results of PA, the gold standard for the diagnosis of pulmonary emboli.
Results: Results of LECFD were positive for DVT in seven of 16 cases of angiographically documented PE. Thus the "sensitivity" of LECFD as a diagnostic aid in cases of suspected PE is 44%. The results of LECFD and V/Q scans were combined and compared with the results of PA. A high-probability V/Q scanning result was considered positive for PE. Intermediate- and low-probability scanning results were considered negative, because in the literature the decision to begin heparin therapy is not made on the basis of this result. The combination of test results was considered positive if either test result was positive and negative only if results of both were negative. With these criteria the combination of test results was positive in only 62% of cases of angiographically documented PE.
Conclusions: If treatment of suspected PE were based on LECFD alone or on duplex combined with V/Q scanning, 40% to 50% of patients with PE would remain untreated. In cases of suspected PE where these noninvasive tests do not confirm its presence, PA should be performed.