Von Willebrand factor antigen as a marker of disease activity in childhood-onset antineutrophil cytoplasmic antibody-associated vasculitis

Objective: Von Willebrand factor (VWF) antigen plays a role in vascular inflammation and thrombosis, both of which are important in the pathogenesis of ANCA-associated vasculitis (AAV). Previous work found that VWF correlates with disease activity in childhood-onset primary CNS vasculitis. We sought to determine the relationship between VWF and disease activity over time in children with AAV. Methods: AAV patients with more than one VWF level measured were included in this retrospective study, and the relationships between active vasculitis, VWF and other disease measures were analysed. Generalized estimating equations analysis was used to account for repeated VWF measurements within a patient. Repeated measures correlation was used to determine associations of paired laboratory observations. Diagnostic performance was evaluated using receiver operating curve analysis. Results: A total of 732 total VWF measurements were collected in 33 AAV patients. VWF antigen levels were higher during active disease [median 2.03 IU/ml, interquartile range (IQR) 1.35, 2.55] compared with inactive disease (median 1.18 IU/ml, IQR 0.94, 1.53). VWF antigen was the only variable that was significantly associated with active disease (odds ratio 3.01, P < 0.001, 95% CI 2.3, 3.93). The effect of VWF did not show a substantial difference between the disease subtypes. There was a moderate positive correlation between VWF antigen and disease activity, with an acceptable sensitivity and specificity rates. Conclusion: Increased VWF antigen levels correlate with active vasculitis in this paediatric-onset AAV cohort and may be used as an additional biomarker in childhood AAV.