ArticlesNon-invasive diagnosis of venous thromboembolism in outpatients
Introduction
Venous thromboembolism is a common and potentially fatal disease.1 Novel diagnostic instruments are useful for both suspected pulmonary embolism (PE) and suspected deep-vein thrombosis (DVT). The plasma concentration of D-dimer, a degradation product of cross-linked fibrin, is almost always raised in the event of an acute DVT or PE; therefore, a normal D-dimer concentration measured by ELISA almost rules out acute venous thromboembolism.2, 3, 4, 5 Moreover, new rapid ELISAs are now available,6, 7, 8, 9 better suited for use in an emergency situation than the classic and more labour-intensive ELISA. Lower-limb venous compression ultrasonography is widely used to detect symptomatic proximal DVT (sensitivity and specificity higher than 97%10, 11). However, the sensitivity of ultrasonography for diagnosis of distal DVT is substantially lower. Hence, various strategies based on serial plethysmography or ultrasonography have been assessed, all requiring the repetition of the examination from two to five times over a period of 7–14 days12, 13, 14, 15, 16, 17, 18, 19 to detect the eventual proximal extension of a distal DVT.20, 21 Lower-limb ultrasonography has also proved useful in patients with suspected PE, since a residual DVT can be shown by ultrasonography in 30–50% of patients with PE.5, 22 Finally, the clinical likelihood of DVT or PE can be estimated either empirically (suspected PE23) or by a score (suspected DVT19, 24). The value of clinical assessment of patients with suspected venous thromboembolism19, 23, 24, 25 has also been recognised. PE may be satisfactorily ruled out by the combination of a low clinical probability of PE and a low-probability lung scan on the grounds of both theoretical25 and clinical23 evidence. The clinical probability of DVT can also be combined with ultrasonography to reduce the need for phlebography.19
We designed a prospective outcome study to validate a simple diagnostic algorithm for suspected venous thromboembolism combining clinical probability assessment, a rapid D-dimer ELISA, a single lower-limb venous ultrasonography, and lung scan, to reduce the need for phlebography and angiography. Since untreated PE or DVT will result in a high frequency of recurrences,26, 27 all patients were followed up for 3 months to assess the safety of the management strategy.
Section snippets
Patients
We studied prospectively 1102 consecutive patients presenting with clinically suspected PE or DVT at the emergency centre or the outpatient clinics of the University Hospital of Geneva, Geneva, Switzerland, and the Hôpital Saint-Luc, Montreal, Canada, between Nov 1, 1996, and Oct 31, 1997. Inclusion criteria were clinical suspicion of DVT or PE and age older than 16 years. Exclusion criteria were refusal or inability to consent to the study (n=24); continuing anticoagulation at onset of
Results
The series included 918 patients (745 from Geneva; 173 from Montreal). The median age was 61 years (range 19–97) for the entire group and did not differ between patients with suspected PE and those with suspected DVT (table 1). The prevalence of venous thromboembolism was 23%, and was similar in patients with suspected DVT (111 [23%] of 474) and PE (104 [23%] of 444).
Discussion
In this series, a diagnosis could be established non-invasively in 863 (94%) of 918 patients with clinically suspected venous thromboembolism referred to an emergency centre. In the strategy studied, two potentially widely available instruments (D-dimer measurement and ultrasonography) were used at the beginning of the diagnostic work-up, and clinical assessment was combined with ultrasonography and lung scan. The strategy proved safe, with a low thromboembolic risk during the 3-month
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