Duplex scan for deep vein thrombosis--defining who needs an examination of the contralateral asymptomatic leg.

OBJECTIVES: Determine the prevalence and clinical significance of deep venous thrombosis (DVT) in the asymptomatic contralateral extremity of patients referred to the vascular laboratory with unilateral symptoms and DVT confirmed by duplex scan.
METHOD: From December 2003 to October 2006, a total of 4813 patients were referred to our vascular laboratory for unilateral venous duplex scans. We prospectively studied 239 patients who were found to have acute DVT and had unilateral symptoms. Contralateral examinations were performed and demographic data, including risk factors for DVT, were entered into a computerized database.
RESULTS: Of the 239 patients, 133 (55.6%) had a major DVT (popliteal vein or above) and 106 (44.4%) had a calf vein DVT. The majority were outpatients (195, 81.6%) and the rest were inpatients (44, 18.4%). The contralateral leg was normal in 192 (80.3%) patients, whereas 47 (19.7%) patients had some evidence of venous thrombosis. These thromboses consisted of acute major DVT (18/47, 38.3%), acute calf vein DVT (14/47, 29.8%), and less clinically significant chronic or superficial thrombus (15/47 (31.9%). All 18 patients with major contralateral DVT had underlying risk factor for thrombosis: active malignancy (12/18), recent surgery (4/18), or trauma (2/18). Patients with asymptomatic contralateral calf vein involvement often had thrombotic risk factors (10/14) but occasionally did not (4/14). Patients with an active malignancy were significantly more likely to have DVT in the asymptomatic leg (18/47, 38.3%) than were patients without cancer (23/192, 12%; both P < .0001). Inpatients were much more likely to have contralateral asymptomatic thrombosis (15/44, 34.1%) than outpatients (31/195, 15.9%; both P < .006). If treatment had been based on the findings in the symptomatic leg, all but 2 of the 239 patients would have been adequately treated. These two patients had multiple thrombotic risk factors that should have precluded ordering of a unilateral examination.
CONCLUSIONS: Inpatients have a very high incidence of clinically silent contralateral thrombosis (34%) and should usually undergo bilateral examinations. Patients with active malignancy have a 38% incidence of asymptomatic contralateral clot and should always have a bilateral study. Outpatients with unilateral symptoms and no associated risk factors for thrombosis can safely undergo unilateral examinations and should be adequately treated according to the unilateral findings. Algorithms to select patients for limited studies should include screening data for active malignancy, recent trauma or surgery, pregnancy, hormone therapy, or history of thrombophilia.