Diagnostic Efficacy of Impedance Plethysmography for Clinically Suspected Deep-Vein Thrombosis

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Abstract
Impedance plethysmography is an accurate noninvasive method to test for proximal vein thrombosis, but it is insensitive to calf-vein thrombi. Patients on referral with clinically suspected deep-vein thrombosis, and normal impedance plethysmographic findings were randomly assigned to either serial impedance plethysmography alone or combined impedance plethysmography and leg scanning (which was shown to be essentially as sensitive as venography) and compared the long-term outcomes. During the initial surveillance, deep-vein thrombosis was detected in 6 of 311 patients (1.9%) tested by serial impedance plethysmography alone and in 30 to 323 patients (9.3%) (most with calf-vein thrombi) tested by the combined approach (P < 0.001). During long-term follow-up, no patient died from pulmonary embolism; but 6 patients (1.9%; 95% confidence limits, 0.7%-4.2%) tested by serial impedance plethysmography developed deep-vein thrombosis compared with 7 patients (2.2% 95% confidence limits, 0.9%-4.4%) tested by the combined approach. Serial impedance plethysmography used alone is an effective strategy to evaluate such symptomatic patients.