Influence of blood group, von Willebrand factor levels, and age on factor VIII levels in non-severe haemophilia A.

ABSTRACT

BACKGROUND: Data on the effect of ABO blood group (ABO), von Willebrand factor (VWF) levels, and age on factor VIII (FVIII) in non-severe haemophilia A (HA) is scarce. OBJECTIVE: To investigate if ABO, VWF levels, and age have an influence on the variability of FVIII levels and consequently on the assessment of severity in non-severe HA. PATIENTS/METHODS: Eighty-nine patients with non-severe HA and 82 healthy controls were included. Data on ABO was collected and FVIII clotting activity (FVIIIC) with one-stage clotting assay (FVIIIC OSA) and chromogenic substrate assay (FVIIIC CSA), FVIII antigen (FVIIIAg) and VWF antigen (VWFAg) and activity (VWFAct) were determined. RESULTS: In HA, FVIIIC OSA and CSA and FVIIIAg were not different between non-O (n = 42, median 15.5, interquartile range 10.4-24.0; 10.0, 6.8-26.0 and 15.2, 10.7-24.9) and O (n = 47, 14.1, 9.0-23.0; 10.0, 5.0-23.0 and 15.2, 9.3-35.5), whereas in healthy controls, non-O individuals had significantly higher FVIII levels. FVIII C showed no relevant correlation with VWF levels in HA, but we observed strong correlations in healthy controls. Age had only a minor influence in HA, but had a considerable impact on FVIIIC in healthy controls. In multivariable regression analysis ABO, VWFAg and age were not associated with FVIIIC in HA, whereas this model explained 61.3% of the FVIIIC variance in healthy controls. CONCLUSIONS: We conclude that in non-severe HA ABO and VWF levels do not substantially influence the variability of FVIII levels and age has only minor effects on it, which is important information for diagnostic procedures.