title: Estimated effect of an integrated approach to suspected deep venous thrombosis using limited-compression ultrasound.
abstract: OBJECTIVE
  Deep vein thrombosis (DVT) is both common and serious, yet the desire to never miss the diagnosis, coupled with the low specificity of D-dimer testing, results in high imaging rates, return visits, and empirical anticoagulation. The objective of this study was to evaluate a new approach incorporating bedside limited-compression ultrasound (LC US) by emergency physicians (EPs) into the workup strategy for DVT.
  
  
  METHODS
  This was a cross-sectional observational study of emergency department (ED) patients with suspected DVT. Patients on anticoagulants; those with chronic DVT, leg cast, or amputation; or when the results of comprehensive imaging were already known were excluded. All patients were treated in the usual fashion based on the protocol in use at the center, including comprehensive imaging based on the modified Wells score and serum D-dimer testing. Seventeen physicians were trained and performed LC US in all subjects. The authors identified a priori an alternate workup strategy in which DVT would be ruled out in "DVT unlikely" (Wells score < 2) patients if the LC US was negative and in "DVT likely" (Wells score ≥ 2) patients if both the LC US and the D-dimer were negative. The criterion standard was based on comprehensive imaging interpreted by radiologists blinded to LC US findings and by structured medical record review at 6 months in patients without comprehensive imaging.
  
  
  RESULTS
  A total of 227 patients were enrolled (47% DVT likely), of whom 24 had DVT. The LC US was positive in 27 cases (21 actually DVT positive), indeterminate in 28 (one DVT positive), and negative in 172 (two DVT positive). Of 130 patients deemed DVT negative by the new strategy, one had confirmed DVT (miss rate = 0.8%; 95% confidence interval [CI] = 0.1% to 4.0%), but this patient had been misclassified by the treating physician as low risk by Wells criteria. The stand-alone sensitivity and specificity of LC US were 91% (95% CI = 70% to 98%) and 97% (95% CI = 92% to 99%), respectively. Incorporating LC US into the diagnostic approach would have reduced the rate of comprehensive imaging from 70% to 43%, D-dimer testing from 100% to 33%, and the mean time to diagnostic certainty by 5.0 hours and avoided 24 (11%) return visits for imaging and 10 (4.4%) cases of unnecessary anticoagulation. In 19% of cases, the treating and scanning physician disagreed whether the patient was DVT likely or DVT unlikely based on Wells score (κ = 0.62; 95% CI = 0.48 to 0.77).
  
  
  CONCLUSIONS
  Limited-compression US holds promise as one component of the diagnostic approach to DVT, but should not be used as a stand-alone test due to imperfect sensitivity. Tradeoffs in diagnostic efficiency for the sake of perfect sensitivity remain a difficult issue collectively in emergency medicine (EM), but need to be scrutinized carefully in light of the costs of overinvestigation, delays in diagnosis, and risks of empirical anticoagulation.
authors.affiliation: The Department of Emergency Medicine, Queen's University, Kingston, Ontario, Canada; The Department of Emergency Medicine, Saint Michael's Hospital, Toronto, Ontario, Canada.
authors.forename: Rachel A
authors.initials: RA
authors.lastname: Poley
authors.forename: Joseph L
authors.initials: JL
authors.lastname: Newbigging
authors.forename: Marco L A
authors.initials: ML
authors.lastname: Sivilotti
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000032:analysis; D003430:Cross-Sectional Studies; D003937:Diagnosis, Differential; D004636:Emergency Service, Hospital; D005260:Female; D005338:Fibrin Fibrinogen Degradation Products / Q000032:analysis; D006801:Humans; D008297:Male; D008875:Middle Aged; D019095:Point-of-Care Systems; D011312:Pressure; D012680:Sensitivity and Specificity; D013997:Time Factors; D014463:Ultrasonography; D020246:Venous Thrombosis / Q000000981:diagnostic imaging*
chemical_list: D015415:Biomarkers; D005338:Fibrin Fibrinogen Degradation Products; C036309:fibrin fragment D