Evaluation of a new automated ELISA test for von Willebrand factor using two monoclonal antibodies

A new automated quantitative enzyme linked immunosorbent assay (ELISA) for the detection of human von Willebrand factor (vWF), VIDAS vWF, has been developed for use on the VIDAS analyser (bioMérieux). The two-step capture/tag test relies on two monoclonal antibodies (mAbs), the second one being labelled with alkaline phosphatase. The lower limit of detection of the assay is < 1 IU/dl, and the upper limit of detection is 120 IU/dl. There is no hook effect for concentrations up to 1100 IU/dl. Intra- and inter-assay precision ranges from 3% and 5%. Assays are performed preferentially using citrated plasma and in these conditions the 95% confidence intervals for normal values are 52-154 IU/dl and 60-200 IU/dl for O blood group and non-O blood group subjects, respectively. Using the lower limits of the normal range as the cut-off level, all patients tested with type 1 (n = 29) or 3 (n = 2) von Willebrand disease (vWD) would be accurately classified with the new ELISA. Comparing the VIDAS test with a conventional ELISA gave a good correlation and comparable results with type 1 and 3 vWD patients (n = 31; r = 0.99; y = 0.99x + 0.24), type 2A and 2B vWD patients (n = 20; r = 0.99; y = 1.05x-1.65) and normal subjects (n = 204; r = 0.94; y = 1.06x-2.6).