Analytical performances of the D-dimer assay for the Immulite 2000 automated immunoassay analyser

We evaluated the analytical performances of a new commercial chemiluminescent enzyme immunometric assay for d-dimer measurement on the Immulite 2000 automated analyser. The within- and between-run coefficients of variations for low, intermediate and high d-dimer concentrations ranged from 2.2% to 5.1% and from 2.9% to 6.0% respectively. The assay was proven linear in a range of d-dimer concentrations comprised between 324 and 7602 ng/ml. Comparison of samples collected in either 0.109 mol/l sodium citrate or lithium-heparin tubes by Bland-Altman plots and nonparametric regression analysis (y = 0.858x - 39, r = 0.997; P < 0.0001) revealed a minimum bias, almost completely attributable to the dilution effect of the anticoagulant. Results of 56 outpatients' citrated plasma samples analysed with the Immulite 2000 d-dimer assay were compared with those of the current reference commercial immunoassay on the Mini Vidas Immunoanalyser. Although the nonparametric regression according to the method of Passing and Bablok and the relative Spearman's correlation coefficient was satisfactory (Immulite = 1.001 x Vidas - 181; r = 0.937, P < 0.001), some random discrepancies could be observed in Bland-Altman plots analysis. The analytical accuracy, calculated as the area under the Receiver Operating Characteristic (ROC) curve (AUC), was 0.961 (P < 0.0001). On the basis of the results of the present evaluation, we conclude that the analytical performances and the main technical features of new Immulite 2000 d-dimer assay make it a suitable method for the rapid quantification of d-dimer in clinical laboratories.