A COMPARISON OF REAL-TIME COMPRESSION ULTRASONOGRAPHY WITH IMPEDANCE PLETHYSMOGRAPHY FOR THE DIAGNOSIS OF DEEP-VEIN THROMBOSIS IN SYMPTOMATIC OUTPATIENTS

Background. Impedance plethysmography performed serially over a one-we ek period has been shown to be an effective diagnostic strategy for pa tients with clinically suspected acute deep-vein thrombosis. Compressi on ultrasonography has a high sensitivity and specificity for the dete ction of proximal-vein thrombosis. The clinical value of repeated ultr asonography in the management of symptomatic deep-vein thrombosis is u nknown. Methods. We conducted a randomized trial in 985 consecutive ou tpatients with clinically suspected deep-vein thrombosis to compare th e diagnostic value of serial impedance plethysmography (494 patients) and serial compression ultrasonography (491 patients). We compared the positive predictive values of both tests for the diagnosis of venous thrombosis, using contrast venography as a reference. The frequencies of venous thromboembolism during a six-month follow-up period were als o compared in patients with repeatedly normal results in order to eval uate the safety of withholding anticoagulant therapy from such patient s. Results. The positive predictive value of an abnormal ultrasonogram was 94 percent (95 percent confidence interval, 87 to 98 percent), wh ereas the predictive value of impedance plethysmography was 83 percent (95 percent confidence interval, 75 to 90 percent) (P = 0.02). In pat ients with repeatedly normal results, the incidence of venous thromboe mbolism during the six-month follow-up period was 1.5 percent (95 perc ent confidence interval, 0.5 to 3.3 percent) for serial compression ul trasonography, as compared with 2.5 percent (95 percent confidence int erval, 1.2 to 4.6 percent) for serial impedance plethysmography. Concl usions. In making the diagnosis of deep-vein thrombosis in symptomatic outpatients, serial compression ultrasonography is preferable to impe dance plethysmography, in view of its superior performance in detectin g venous thrombosis.