PB1848 CAN VON WILLEBRAND ANTIGEN LEVEL AT THE INITIAL PRESENTATION BE ABLE TO PREDICT THE INHIBITOR DEVELOPMENT IN PATIENTS WITH SEVERE HEMOPHILIA A?

Background: There is a large heterogeneity in bleeding events and arthropaty among patients with severe Hemophilia A which is multifactorial. Mostly FVIII gene mutations seems to influence phenotype however underlying prothrombotic risk factors and FVIII half life may both have an affect on the heterogeneity.VWF is the specific carrier of factor VIII in plasma and protecs it from proteolytic degradation,prolonging its half life in circulation and efficiently localizing it at the site of vasculary injuiry. Aims: Here, we want to evaluate von Willebrand antigen levels of the children with severe Hemophilia A at the initial diagnose and want to figure out whether low initial von Willebrand antigen (VWF:Ag) levels may asssociated with a frequent bleeding phenotype or not, retrospectively. Methods: We retrospectively evaluate charts of 40 children with severe hemophilia A who was diagnosed in between 1997 and 2017 at the Hacettepe University, Department of Pediatric Hematology. All of these patients were receiving prophylaxis and among those 40 patients only 6 had a history of inhibitor in which 2 of them still persist. Results: Mean VWF:Ag levels were found to be 114 ± 40 (32‐200)IU/dL. Ten out of 40 children VWF:Ag levels was found to be under 100IU/dL and from those 5 out of ten were found to be under 80IU/dL. Interestingly none of them were have the blood group ’O’. Initial bleeding age were found to be lower (median 6 months)in patients with low VWF:Ag (<100IU/dL) than that of the patients with high VWF:Ag (≥100IU/dL)(median 18 months)(p = 0.05).2/10 had a history of inhibitor (1 low titer 1 high titer) development and 7/10 had a target joint which requires radiosyneviectomy during the follow up period.On the other hand 4 out of 30 patients with VWF:Ag>100IU/dL had a history of inhibitor development (4 high titre inhibitor: 2 was still found to be positive) and 5/30 had a target joint. Summary/Conclusion: Despite we do not have the half lifes of FVIII, a significant shorter half life in patients with a low VWF:Ag level was previosly reported. Although there is no follow up of VWF:Ag levels in this small group of patients with a frequent bleeders initial VWF:Ag levels may give some clues about the clinical outcome.