Acquired hemophilia A: an underdiagnosed, severe bleeding disorder

series and single reports. Currently, the most reliable data on its incidence, mortality, and treatment outcome come from prospective national registries: SACHA from France, 4 UKHCDO from United Kingdom, 5 and the pan -European EACH2 registry. 6 In Poland, AHA is currently registered in the national registry of bleeding disorders at the Institute of Hematology and Transfusion Medicine in Warsaw. A special Polish registry of acquired hemophilia is under development and will be managed by the Working Group on Hemostasis of the Polish Society of Hematology and Transfusion Medicine. The first Polish guidelines on the management of AHA were published in 2011 by this Working Group. 2 Pathophysiology AHA is caused by polyclonal inhibitory immunoglobulins G (predominantly IgG1 and IgG4) against FVIII. They react with A2, A3, or C2 domains of the FVIII molecule, blocking its interactions with active factor IX, phospholipids, and von Willebrand factor. 7 A disturbed proportion of CD4+ Th1 to Th2 cells plays a role in autoantibody production and reactivity. Predominance of Th2 -driven IgG subclasses is associated with higher inhibitor titer and poor outcome, whereas the predominance of Th1 -driven IgG correlates with better outcome of immunosuppressive therapy. 8 Introduction Massive hemorrhage in a patient without underlying congenital bleeding disorder may have a number of causes, including intake or overdose of anticoagulant agents, acquired vascular or platelet bleeding disorders (e.g., autoimmune thrombocytopenia), or acquired deficiency of clotting factors. Urgent differential diagnosis and specific treatment are often crucial.