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BACKGROUND: The modulation of Factor (F)VIII activity (FVIII : C), von Willebrand factor antigen (VWF : Ag), and von Willebrand factor ristocetin cofactor (VWF : RCo) by the ABO(H) blood group is well established in adults. Expression of ABH antigens on N-linked glycans of VWF protects plasma VWF from proteolysis and clearance. Protection by H antigens is less effective than by AB antigens, resulting in approximately 25% lower VWF plasma levels in adults with blood group O compared to non-O. Given the reduced branching of ABO(H) bearing structures (I blood group system) with lower numbers of H, A, and B antigen sites during the first 18 months of life, we reasoned that if the relationship between ABO(H) blood group and VWF levels were causal, the difference of ABO(H) blood group–dependent VWF levels should be marginal or not be observed in the first months of life.

STUDY DESIGN AND METHODS: We undertook quantification of FVIII : C and VWF in 574 presumably healthy children aged 1 to 210 months and correlated the values with ABO(H) blood type. Moreover, we establish reference intervals for common coagulation variables for several pediatric age groups.

RESULTS: Significant differences between blood group O versus non-O values of FVIII : C, VWF : Ag, and VWF : RCo were not observed in the first months of life, started to develop during childhood, and in adolescence reached adult values.

CONCLUSION: In comparison to the levels for adults and adolescents, we report fundamental differences of VWF levels in the first year of life, which may be associated with the physiologic development of the ABO(H) and I blood group system.