REEVALUATION OF THE SENSITIVITY OF IMPEDANCE PLETHYSMOGRAPHY FOR THE DETECTION OF PROXIMAL DEEP-VEIN THROMBOSIS

Background: To reevaluate the sensitivity of impedance plethysmography (IPG) for proximal deep vein thrombosis (DVT) and to establish a rela tionship between the location and size of thrombi and the results of I PG. Design: Prospective cohort study. Methods: One hundred thirty-two consecutive patients with clinically suspected DVT underwent IPG testi ng and most (n=118) underwent contrast-enhanced venography; in 14 pati ents, venous ultrasonography was performed and demonstrated definitive proximal DVT in which the size and extent of the thrombus could be de lineated. All patients with dubious or normal ultrasound results under went contrast-enhanced venography. All tests were performed and test r esults were interpreted without knowledge of the results of the other tests. Patients were considered to have proximal DVT if this was demon strated on venography or ultrasound, calf DVT if this was demonstrated on venography, or no DVT if venography yielded normal findings. The s ensitivity and specificity of IPG for DVT were calculated. Results: Of the 132 patients, 40 (30%) had proximal DVT, seven (5%) had calf DVT, and 85 (64%) had no DVT. The sensitivity of IPG for proximal DVT was 65% and the specificity was 93%. Of the proximal vein thrombi, IPG det ected three (23%) of 13 that involved the popliteal vein but not the s uperficial femoral vein and 23 (85%) of 27 proximal vein thrombi that involved the superficial femoral vein. Conclusions: Our study demonstr ated that the sensitivity of IPG for proximal DVT at our center is onl y 65%, a figure that is much lower than those reported in earlier stud ies from our institution. We hypothesize that because of a change in r eferral practice, an increased proportion of patients with less severe symptoms are now referred to our center than in the past. These patie nts have thrombi that are smaller, less likely to be occlusive, and th erefore less likely to yield abnormal IPG findings.