Validation of a new D-dimer microparticle enzyme immunoassay (AxSYM D-Dimer) in patients with suspected pulmonary embolism (PE).

OBJECTIVES: The aim of the study was to evaluate a new automated assay for D-dimer testing (AxSYM D-Dimer) based on microparticle enzyme-immunoassay technology by comparing it with three well established D-dimer assays.

PATIENTS AND METHODS: The performance of the new assay was evaluated in 280 plasma samples that were collected prospectively from out-patients included in a management study evaluating a decision based algorithm.

RESULTS: 58/280 patients (21%) had PE diagnosed by CT. Median values of AxSYM D-dimer in patients with PE were 3689 ng/mL (range 775-9000). Comparison analysis displayed excellent agreement with VIDAS (kappa=0.84) and Asserachrom (kappa=0.81) D-dimer assays. A strong correlation was found between AxSYM and the VIDAS (r=0.96) and Asserachrom (r=0.89) D-dimer assays. The highest cut-off value for AxSYM that yielded a sensitivity of 100% was 765 ng/mL with a specificity of 50%. At the cut-off level <500 ng/mL, the sensitivity and specificity of AxSYM D-dimer were 100% and 34%; VIDAS 100% and 42%; Asserachrom 100% and 40%; and STALiatest 100% and 37%, respectively. AxSYM D-dimer was negative in 75 patients (33.8%). None of these had PE at the initial work-up or VTE during the 3-month follow-up.

CONCLUSIONS: AxSYM D-dimer seems to be safe and effective in ruling out PE in out-patients. The cut-off level can be set at 500 to 750 ng/mL, at which the assay displays a performance that is comparable to that of the ELISA based assays. However, further studies are needed to confirm the safety of the assay and to determine the most optimal cut-off level in patients with venous thromboembolism.