Comparison of D-Dimer PLUS assay with NycoCard D-Dimer

Measurement of D-dimer levels has gained widespread use in the diagnosis of various clinical situations that relate to thrombosis and fibrinolysis. Nowadays, different rapid and fully automated quantitative D-Dimer assays that can be performed on coagulation analyzers are commercially available. The aim of our study was to compare two rapid and quantitative D-Dimer assays based on different methodology: NycoCard D-Dimer (Axis-Shield, Oslo, Norway) based upon the immunometric flowthrough principle with a new fully automated latex-enhanced turbidimetric test D-Dimer PLUS (Dade Behring, Marburg, Germany). D-dimer concentrations were measured in fresh plasma samples of 56 patients with request for the determination of D-dimer, using the NycoCard D-Dimer on NycoCard READER II. Samples were frozen for later measurement of D-dimer with the D-Dimer PLUS assay on a BCS analyzer. Results obtained with NycoCard D-Dimer ranged from 0.1 to > 20.0 mg/L (cut-off value 0.3 mg/L) whilst the results obtained with D-Dimer PLUS ranged from 0.06 to 6.01 mg/L (cut-off value 0.19 mg/L). The relationship between D-Dimer PLUS and NycoCard showed a correlation coefficient (r) of 0.713 with a regression equation of y = 0.3 x + 0.18. The majority of D-dimer levels were comparable between assays, being approximately two to three times higher with Nycocard D-Dimer as compared to D-Dimer PLUS. The greatest discrepancy between results was found above the cut-off value (in the range of 0.3-0.5 mg/L) for Nycocard D-Dimer: normal D-dimer levels (range 0.12-0.18 mg/L) were obtained in 7 out of 14 plasma samples with D-Dimer PLUS.The results show that the standardization of D-Dimer assay is crucial and that discrepancy in the obtained results can be due to different calibrators and different monoclonal antibodies used (DD5 vs. S4H9) as well as different cut-off values applied.