PB0814 - How do laboratories perform von Willebrand disease (VWD) diagnostics?

Background: Dysfunction or absence of von Willebrand factor (VWF) may lead to von Willebrand disease (VWD), which is a common inherited bleeding disorder. VWD is classified in 3 types: type 1 is a partial quantitative deficiency of VWF, type 3 is a complete quantitative deficiency of VWF and type 2 consist of qualitative abnormalities of VWF. To come to a correct VWD diagnosis multiple tests and a correct interpretation of these tests are needed.

Aims: The aim of the study was to gain insight into the approach of laboratories towards the VWD diagnosis with respect to the used algorithm, tests, cut-off values and the applied guidelines.

Methods: Data from two samples of the external quality assessment (EQA) VWF surveys of the ECAT were evaluated. The classification of the samples by the participants were compared with the measurements found for various VWF parameters. Furthermore, results were analysed of a questionnaire that was sent to haemostasis laboratories about the performance of VWD diagnostic approaches.

Results: The majority of participants indicated the correct classification for the two samples used in the EQA program. However, respectively 6 and 23% indicated another classification. For both samples significant differences were observed in the measurements of the VWF parameters divided by the classification of the participants, e.g. for VWF:RCo/VWF:Ag ratio (Fig. 1). The questionnaire demonstrated that the testing approach varied between the laboratories, especially the parameters that were essential for the discrimination between VWD type 1 and healthy individuals and the cut-off values used to discriminate between VWD type 1 and 2.

Conclusion(s): Diagnosis of VWD is heterogeneous in approach with significant differences in VWF measurements, used guidelines and as a consequence differences in applied cut-off values. This will cause differences in the diagnosis of VWD and treatment of patients. Harmonization of approaches is needed.