Inhibitors are a serious medical problem that can occur when a person with hemophilia has an immune response to treatment with clotting factor concentrates.
The immune system defends the body from harmful germs and viruses. Sometimes a person's immune system reacts to proteins in factor concentrates as if they were harmful foreign substances because the body has never seen them before. When this happens inhibitors form in the blood to fight against the foreign factor proteins. This stops the factor concentrates from being able to fix the bleeding problem.
Bleeding is very hard to control in someone with inhibitors. If bleeding into the muscles and joints is not controlled, permanent joint damage is likely. Treatment of inhibitors is one of the biggest challenges in hemophilia care today.
Approximately 5-8% of people with mild or moderate hemophilia A develop inhibitors.
Approximately 2-3% of people with hemophilia B develop inhibitors.