Hemophilia is treated by replacing the missing clotting proteins (factor VIII or factor IX). This is called factor replacement therapy. However, some people with hemophilia do not have a good response to these factors. This is because their bodies inhibit or stop the factor from working.
Because the clotting proteins or factors used in the treatment of hemophilia are from outside of the body there is always the risk that the body's immune system will see those factors as foreign invaders and attack them with antibodies.
Normally, antibodies help protect the body by destroying harmful substances, such as bacteria. But in some patients antibodies are activated when factor is infused to treat a bleed.
An antibody that attacks factor VIII or IX that has been infused to treat hemophilia is called an inhibitor. When inhibitors attack the factor replacement therapy the therapy is neutralized, bleeding is difficult to control, and alternative treatments need to be considered.
