Factor activity levels and bleeding scores in hemophilia carriers: apparent paradoxes

Multiple studies report abnormal bleeding in hemophilia carriers with normal factor activity levels. Other studies report the lack of abnormal bleeding in carriers with hemophilia. In addition, limited data suggests that the bleeding risk in carriers increases with age while at the same time, factor activity levels are rising. Potential explanations for these paradoxical findings include inadequate data, inadequate measures of bleeding, inadequate measures of factor activity, or uncharacterized biological modifiers.