title: Reevaluation of the sensitivity of impedance plethysmography for the detection of proximal deep vein thrombosis.
abstract: BACKGROUND
  To reevaluate the sensitivity of impedance plethysmography (IPG) for proximal deep vein thrombosis (DVT) and to establish a relationship between the location and size of thrombi and the results of IPG.
  
  
  METHODS
  Prospective cohort study.
  
  
  METHODS
  One hundred thirty-two consecutive patients with clinically suspected DVT underwent IPG testing and most (n = 118) underwent contrast-enhanced venography; in 14 patients, venous ultrasonography was performed and demonstrated definitive proximal DVT in which the size and extent of the thrombus could be delineated. All patients with dubious or normal ultrasound results underwent contrast-enhanced venography. All tests were performed and test results were interpreted without knowledge of the results of the other tests. Patients were considered to have proximal DVT if this was demonstrated on venography or ultrasound, calf DVT if this was demonstrated on venography, or no DVT if venography yielded normal findings. The sensitivity 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 detected three (23%) of 13 that involved the popliteal vein but not the superficial femoral vein and 23 (85%) of 27 proximal vein thrombi that involved the superficial femoral vein.
  
  
  CONCLUSIONS
  Our study demonstrated that the sensitivity of IPG for proximal DVT at our center is only 65%, a figure that is much lower than those reported in earlier studies from our institution. We hypothesize that because of a change in referral practice, an increased proportion of patients with less severe symptoms are now referred to our center than in the past. These patients have thrombi that are smaller, less likely to be occlusive, and therefore less likely to yield abnormal IPG findings.
authors.affiliation: Department of Medicine, McMaster University, Hamilton, Ontario.
authors.forename: J S
authors.initials: JS
authors.lastname: Ginsberg
authors.forename: P S
authors.initials: PS
authors.lastname: Wells
authors.forename: J
authors.initials: J
authors.lastname: Hirsh
authors.forename: A A
authors.initials: AA
authors.lastname: Panju
authors.forename: M A
authors.initials: MA
authors.lastname: Patel
authors.forename: D E
authors.initials: DE
authors.lastname: Malone
authors.forename: J
authors.initials: J
authors.lastname: McGinnis
authors.forename: P
authors.initials: P
authors.lastname: Stevens
authors.forename: P
authors.initials: P
authors.lastname: Brill-Edwards
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D015331:Cohort Studies; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D008875:Middle Aged; D010690:Phlebography; D010992:Plethysmography, Impedance / Q000592:standards*; D011237:Predictive Value of Tests; D011446:Prospective Studies; D011655:Pulmonary Embolism / Q000175:diagnosis; D012680:Sensitivity and Specificity; D013924:Thrombophlebitis / Q000175:diagnosis* / Q000453:epidemiology; D018084:Ultrasonography, Interventional