Deep vein thrombosis: ultrasound was a better diagnostic test than impedance plethysmography.

Clinical bottom line (level 1b)

  1. In patients with suspected deep vein thrombosis, ultrasound could diagnose and rule out DVT, whereas impedance plethysmography could not alone.
  2. The more non-compressible veins seen on ultrasound, the greater the chance was of DVT.
Wells et al: Thrombosis and Haemostasis 1995; 74 (6): 1423-1427
Expires May 2003

The study

Setting: two university hospitals, Canada and Italy

453 patients (aged range 18 to 87 years; mean 63, 55% female) suspected first episode of deep vein thrombosis

Excluded if
  • previous objectively documented DVT or pulmonary embolism
  • contraindication to contrast media
  • suspected pulmonary embolism
  • pregnant
  • anticoagulated for >48 hours
  • below knee amputation
  • non-thrombotic disorder more likely or symptoms not consistent with a DVT



    • Independent blinded reference standard, applied in all patients from a consecutive appropriate spectrum.
    Reference standard:
    • venogram within 24 hours
    Diagnostic test: 1. impedance plethysmography: 5 inflation-deflation test- positive ig highest rise/fall crossed discrimination line. 2. ultrasound scan by trained sonographer- positive if lack of full compression on any transverse view of common femoral at inguinal ligament, popliteal at knee joint to trifurcation of calf veins

    The evidence

    pre-test probability of deep vein thrombosis: 22%, (95% CI: 19% to 26%)

    diagnostic test DVT no DVT LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    ultrasound scan 95 9 37
    (19 to 71)     		91% 0.11
    (0.061 to 0.19)     		3%
    total 106 371


    diagnostic test DVT no DVT LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    impedance plethysmography 23 24 3.4
    (2.0 to 5.8)     		49% 0.82
    (0.74 to 0.92)     		19%
    total 99 354


    diagnostic test DVT no DVT LR+
    (95% CI)    		 post-test probability LR-
    (95% CI)    		 post-test probability
    2 to 3 abnormal veins on USS 80 0 inf
    (21 to inf)     		100% 0.24
    (0.17 to 0.34)     		6%
    1 abnormal vein 15 7 7.4
    (3.1 to 18)     		68% 0.87
    (0.81 to 0.95)     		20%
    0 abnormal veins 9 349 0.09
    (0.05 to 0.17)     		3% 25
    (15 to 44)     		88%
    inadequate study 1 6 0.57
    (0.07 to 4.7)     		14% 1.01
    (0.98 to 1.0)     		23%
    total 105 362

    • 42/495 venograms were not evaluable (8.5%, 95% CI: 6% to 11%).

    Citation

    1. Wells PS, Hirsh J, Anderson DR, et al: Comparison of accuracy of impedance plethysmography and compression ultrasonography in outpatients with clinically suspected deep vein thrombosis: a two centre paired-design prospective trial. Thrombosis and Haemostasis 1995; 74 (6): 1423-1427
    Contributor: Chris Ball and Clare Wotton, May 2000
    Reviewer:

    Clinical Question.
    Patient suspected DVT
    Intervention or Exposure impedance plethysmography and ultrasound scan
    Comparison venogram
    Outcome diagnosis