Validation of a rapid test (VWF-LIA) for the quantitative determination of von Willebrand factor antigen in type 1 von Willebrand disease diagnosis within the European multicenter study MCMDM-1VWD

Background: Accurate measurement of von Willebrand factor (VWF) is a critical requirement for the diagnosis of von Willebrand disease (VWD). Aim of the study: To evaluate the diagnostic efficiency of a rapid quantitative test for the measurement of VWF antigen (VWF:Ag) in type 1 VWD. Patients and methods: VWF:Ag was measured with an ELISA in a robotic instrument, as a reference method, and with a fully automated latex-immunoassay (LIA) on an ACL 9000 analyser in 1,716 subjects enrolled within the Molecular and Clinical Markers for Diagnosis and Management of Type 1 von Willebrand Disease (MCMDM-1VWD) Study. Among these subjects, 1,049 were healthy controls, 281 healthy family members and 386 affected members from 127 European families with type 1 VWD. Results: The assay linearity range was 10-125 IU/dL for LIA (R2 = 0.99) and 5-133 IU/dL for ELISA (R2 = 0.99). The inter-assay CV for low VWF levels (∼ 30 IU/dL) was 2% for the LIA test and 8.7 % for ELISA. The sensitivity for detection of type 1 VWD affected members was 86% and the specificity 91% for LIA, 87% and 90% for ELISA. A receiver-operator (ROC) analysis disclosed only a marginal difference between the two tests, LIA having a slightly greater area under the curve (0.94 vs. 0.93, p = 0.03). Conclusion: VWF:Ag LIA compared well to standard ELISA in this large population of patients and controls, showing better CV. However the lower detection limit for the VWF:Ag LIA compared to the VWF:Ag ELISA means that the LIA assay is less good at discriminating between type 3 VWD and moderate type 1 VWD.