Serial impedance plethysmography for suspected deep venous thrombosis in outpatients: The Amsterdam general practitioner study: Huisman MV, Buller HR, Ten Cate JW, et al. N Engl J Med 1986;314:823–826

Abstract

Previous studies have indicated that the diagnosis of deep venous thrombosis by clinical signs and symptoms is unreliable. However, the “gold standard” for the diagnosis of deep venous thrombosis, phlebography, is relatively expensive and invasive. Therefore, a reliable noninvasive method to diagnose deep venous thrombosis would be preferable. Between January 1983 and February 1984, 426 consecutive outpatients with clinically suspected acute deep venous thrombosis underwent four sequential impedance plethysmograms on days 1, 2, 5, and 10 after referral. Patients were again tested at 3 and 6 months after referral. In addition, patients suspected of having pulmonary embolization were tested with ventilation perfusion scans and all patients with positive scans underwent pulmonary angiography. Ninety-five percent of patients with abnormal plethysmograms underwent phlebography. Patients with abnormal phlebograms were treated with standard anticoagulant therapy. Patients with four consecutive normal plethysmograms did not receive anticoagulation therapy. The effects of this approach on recurrent deep venous thrombosis, pulmonary embolism, and death were evaluated. Ninety-five percent confidence limits were calculated with the use of the binomial distribution. The results of all four plethysmography studies were normal in 289 patients (68%). One of these patients may have had a minor pulmonary embolus. During the 6-month follow-up, none of these patients died of venous thromboembolism or had suspected pulmonary embolism. Impedance plethysmograms were abnormal in 137 patients (32%); 117 patients (85%) had abnormal results on their first test. Phlebography confirmed deep venous thrombosis in patients with abnormal plethysmograms 92% of the time. This study demonstrates that in outpatients with clinically suspected deep venous thrombosis, normal serial impedance plethysmography can be used to exclude the diagnosis of deep venous thrombosis and consequently to withhold anticoagulant therapy. The data from this study indicate that withholding anticoagulant treatment from patients with serially normal impedance plethysmograms appears to be as safe as withholding anticoagulant treatment from those with normal phlebograms.