Factor VIII Levels in Blood Group O and Non-O in Patients with Non-Severe Haemophilia a
Authors: Rejtoe Judit , Königsbrügge Oliver , Grilz Ella , Hofer Stefanie , Gebhart Johanna , Schuster Gerhard , Feistritzer Clemens , Quehenberger Peter , Ay Cihan , Pabinger Ingrid 
Published: November 2019

Introduction
ABO blood group affects levels of von Willebrand Factor (VWF) and Factor (F) VIII, as individuals with blood group non-O have higher levels of VWF and FVIII. To the best of our knowledge there is no data available regarding the association between blood group and FVIII in non-severe haemophilia.
Aim
We aimed to explore the influence of ABO blood group on VWF and FVIII levels in patients with non-severe haemophilia A (HA).
Methods
We recruited persons with non-severe HA (FVIII levels of 1-40%). Adult patients (age ≥ 18 years), with platelet count > 105 /µl, without impaired renal and hepatic function, active cancer, surgery within the last 6 weeks, or overt infection within the last 2 weeks, who gave their informed consent were included. A blood sample was collected for laboratory analysis.
The diagnosis of haemophilia was confirmed by molecular analysis of the FVIII gene in all patients. None of the patients had inhibitors against FVIII at the time of sample collection. The lowest FVIII level ever measured in each patient's history served as basis for the assessment of severity. Healthy male persons with a median age comparable to the patient group served as controls.
We determined the following parameters: ABO blood group, FVIII, VWF activity (VWF:Act), and VWF antigen (VWF:Ag). FVIII was measured with a one-stage assay (Sysmex-CA7000 - Sysmex, Kobe, Japan, in multi-dilution mode with native FVIII-deficient plasma - Technoclone, Vienna, Austria and Aktin FS activator - Siemens, Marburg, Germany), VWF:Act (BC von Willebrand Reagent or Innovance VWF Ac - Siemens Healthcare, Marburg, Germany) and VWF:Ag levels with a latex agglutination assay (STA LIATEST VWF, Diagnostica Stago).
Comparison of VWF and FVIII levels between blood group O and non-O was calculated with Mann-Whitney-U test, correlation between FVIII and VWF levels was calculated with Spearman's correlation, association of FVIII and VWF separated for blood group was calculated with univariable linear regression. Association of FVIII with VWF and blood group was calculated using multivariable linear regression. All calculations were performed with SPSS (IBM Version 25.0).
Results
A total of 89 persons with HA (71 with mild and 18 with moderate haemophilia) and 82 healthy controls were included. Patient characteristics are listed in Table 1.
Median levels of VWF were significantly higher both in patients (p=0.002 for both VWF:Ag and VWF:Act) and healthy controls (p<0.001 for both VWF:Ag and VWF:Act) with blood group non-O compared to individuals with blood group O. FVIII levels were not significantly different between blood group non-O and O in HA patients (15% vs. 14.1%, p=0.716) but significantly higher in healthy controls with blood group non-O versus O (150.0% vs. 109.5%, p<0.001; Table 2).
In HA there was no correlation between FVIII and VWF:Act (rho=0.180, p=0.095) or between FVIII and VWF:Ag (rho=0.028, p=0.795, Table 3). In univariable linear regression there was no significant association between VWF and FVIII in HA, neither in those with blood group non-O nor in those with blood group O (Figure 1).
Also in multivariable linear regression there was no significant association between VWF (p=0.632) and blood group (p=0.929) with FVIII in patients with HA.
In healthy controls, there was a strong positive correlation between FVIII and VWF:Act (rho=0.751, p<0.001) and between FVIII and VWF:Ag (rho=0.790, p<0.001) (Table 3). In the healthy controls with blood group non-O 1% elevation in the VWF:Ag was associated with 0.63% of elevation in the FVIII:Act and in blood group O 1% elevation in the VWF:Ag was associated with 0.66% of elevation in the FVIII:Act (Figure 2).
Conclusions
Neither the blood group nor the VWF had an influence on FVIII levels in non-severe HA patients. We conclude that the impact of the genetic mutation of the FVIII gene by far outweighs the influence of VWF levels and the blood group. Thus, for the diagnosis of HA and for determination of HA severity, the blood group needs not to be taken into account.

Disclosures
Pabinger: Roche: Honoraria; Sobi: Research Funding; Novo Nordisk: Research Funding; CSL Behring: Research Funding; Pfizer: Honoraria; Shire: Honoraria; Bayer: Honoraria; Sobi: Honoraria.