A new interpretive method for impedance plethysmography

Clinical experience revealed that Wheeler's interpretative method for impedance plethysmography studies resulted in a large number of false negative and borderline interpretations, so a new interpretative method was created using additional impedance plethysmography parameters. This study was performed to compare this new method with Wheeler's method in 21 patients with suspected deep venous thrombosis. The accuracy of each method was determined by comparing the impedance plethysmography interpretations with venography. The patients were divided into groups according to venogram results of no thrombosis, and tibial (calf) venous thrombosis. Nine of the 21 patients had no thrombosis on venogram. Wheeler's method and the new method both resulted in 56% true-negative interpretations. Twelve of the 21 patients had proximal deep venous thrombosis and/or tibial venous thrombosis on venogram. Wheeler's method resulted in 8% true-positive interpretations and 17% false-negative interpretations. Of the patients in the study, 62% had borderline interpretations. The new method resulted in 75% true-positive interpretations and no false-negatives. The new method decreased the borderline interpretations to 33%. By calculating a basal impedance difference between the patient's two legs, the new method did provide guidelines that could identify patients with borderline interpretations who would require additional testing. The new impedance plethysmography interpretative method did lower the number of borderline and false-negative interpretations, and it provided guidelines to identify patients with borderline interpretations who need further testing.