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) and an established quick test (Nycocard D-dimer assay) in the diagnosis of deep vein thrombosis (DVT) compared with ultrasonography. A third assay (Auto Dimer) became available during sample collection and has been included in the final assessment. The diagnostic performance of the Auto Dimer 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 and Auto Dimer) showed sensitivities of 90 and 88%, specificities of 42 and 44%, and NPV's of 85 and 83%, respectively. The Nycocard D-dimer assay showed a sensitivity of 63%, specificity of 67% and NPV of 71%.

CONCLUSIONS

The diagnostic performance of VIDAS New and the Auto Dimer 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. Abbreviations DVT, deep venous thrombosis, NPV, negative predictive value, PPV, positive predictive value