If DVT is not detected, there is uncertainty whether patients should be anticoagulated. If a decision is made not to anticoagulate, there is the option of doing one or more follow-up US examinations of the legs to detect (and then treat) evolving proximal DVT.110,114 Serial testing for proximal DVT has been shown to be a safe management strategy in patients with suspected PE who have nondiagnostic ventilation-perfusion scans, many of whom are expected to have subsegmental PE.110,111,120 We suggest that a diagnosis of subsegmental PE is more likely to be correct (ie, a true positive) if: (1) the CT pulmonary angiogram is of high quality with good opaci cation of the distal pulmonary arteries; (2) there are multiple intraluminal defects; (3) defects involve more proximal subsegmental arteries (ie, are larger); (4) defects are seen on more than one image; (5) defects are surrounded by contrast rather than appearing to be adherent to the pulmonary artery walls; (6) defects are seen on more than one projection; (7) patients are symptomatic, as opposed to PE being an incidental nding; (8) there is a high clinical pretest probability for PE; and (9) D-dimer level is elevated, particularly if the increase is marked and otherwise unexplained. In addition to whether or not patients truly have subsegmental PE, we consider the following to be risk factors for recurrent or progressive VTE if patients are not anticoagulated patients who: are hospitalized or have reduced mobility for another reason; have active cancer (particularly if metastatic or being treated with chemotherapy); or have no reversible risk factor for VTE such as recent surgery. Furthermore, a low cardiopulmonary reserve or marked symptoms that cannot be attributed to another condition favor anticoagulant therapy, whereas a high risk of bleeding favors no anticoagulant therapy. 