F9 and hemophilia B: The diagnosis is confirmed by measuring factor VIII levels in hemophilia A and factor IX levels in hemophilia B. The differential diagnosis of hereditary hemophilia should include von Willebrand disease, in which the factor VIII deficiency is secondary to a qualitative or quantitative defect of its carrier protein (von Willebrand factor), as well as acquired hemophilia, which will be discussed later [4,22,23].