Validity of D-dimer tests in the diagnosis of deep vein thrombosis: a prospective comparative study of three quantitative assays

Objectives. To assess the diagnostic reliability of a new quantitative D-dimer assay (VIDAS New((R)) ) and an established quick test (Nycocard((R)) D-dimer assay) in the diagnosis of deep vein thrombosis (DVT) compared with ultrasonography. A third assay (Auto Dimer((R)) ) became available during sample collection and has been included in the final assessment. The diagnostic performance of the Auto Dimer((R)) assay was evaluated on three different coagulation analysers. Design. A clinical prospective study of patients admitted to hospital for evaluation of DVT. Setting. The admission ward at Aalborg Hospital. Subjects. A total of 113 outpatients with suspected DVT. Main outcome measures. Compression ultrasonography was used as the reference method for a diagnosis of DVT and compared with different D-dimer assays. The results were expressed as sensitivity, specificity, positive predictive value and negative predictive value (NPV). Results. Deep vein thrombosis was established in 49 patients (43%). Two D-dimer assays (VIDAS New((R)) and Auto Dimer((R)) ) showed sensitivities of 90 and 88%, specificities of 42 and 44%, and NPV's of 85 and 83%, respectively. The Nycocard((R)) D-dimer assay showed a sensitivity of 63%, specificity of 67% and NPV of 71%. Conclusions. The diagnostic performance of VIDAS New((R)) and the Auto Dimer((R)) D-dimer assays is almost identical, but this study suggests that neither of the D-dimer assays is suitable as the only screening method for DVT, in a situation with a high pretest probability of DVT. This call for a differential strategy that distinguishes between cases of low and high clinical probability using either a D-dimer test or ultrasonography.