title: A comparison of real-time compression ultrasonography with impedance plethysmography for the diagnosis of deep-vein thrombosis in symptomatic outpatients.
abstract: BACKGROUND
  Impedance plethysmography performed serially over a one-week period has been shown to be an effective diagnostic strategy for patients with clinically suspected acute deep-vein thrombosis. Compression ultrasonography has a high sensitivity and specificity for the detection of proximal-vein thrombosis. The clinical value of repeated ultrasonography in the management of symptomatic deep-vein thrombosis is unknown.
  
  
  METHODS
  We conducted a randomized trial in 985 consecutive outpatients with clinically suspected deep-vein thrombosis to compare the 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 also compared in patients with repeatedly normal results in order to evaluate the safety of withholding anticoagulant therapy from such patients.
  
  
  RESULTS
  The positive predictive value of an abnormal ultrasonogram was 94 percent (95 percent confidence interval, 87 to 98 percent), whereas the predictive value of impedance plethysmography was 83 percent (95 percent confidence interval, 75 to 90 percent) (P = 0.02). In patients with repeatedly normal results, the incidence of venous thromboembolism during the six-month follow-up period was 1.5 percent (95 percent confidence interval, 0.5 to 3.3 percent) for serial compression ultrasonography, as compared with 2.5 percent (95 percent confidence interval, 1.2 to 4.6 percent) for serial impedance plethysmography.
  
  
  CONCLUSIONS
  In making the diagnosis of deep-vein thrombosis in symptomatic outpatients, serial compression ultrasonography is preferable to impedance plethysmography, in view of its superior performance in detecting venous thrombosis.
authors.affiliation: Center for Hemostasis, Thrombosis, Atherosclerosis and Inflammation Research, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: H
authors.initials: H
authors.lastname: Heijboer
authors.forename: H R
authors.initials: HR
authors.lastname: Büller
authors.forename: A W
authors.initials: AW
authors.lastname: Lensing
authors.forename: A G
authors.initials: AG
authors.lastname: Turpie
authors.forename: L P
authors.initials: LP
authors.lastname: Colly
authors.forename: J W
authors.initials: JW
authors.lastname: ten Cate
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D016001:Confidence Intervals; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010992:Plethysmography, Impedance; D011237:Predictive Value of Tests; D013923:Thromboembolism / Q000175:diagnosis / Q000000981:diagnostic imaging; D013924:Thrombophlebitis / Q000175:diagnosis / Q000000981:diagnostic imaging*; D014463:Ultrasonography