Hemophilia: Inhibitors

About Inhibitors

Inhibitors are antibodies in the immune system — cells that detect and fight off foreign substances in the body. In most instances, antibodies are helpful in detecting and fighting off diseases. Unfortunately, antibodies can form against the replacement clotting factor that is infused to control bleeding. When factor is infused into the body to stop bleeding, the immune system recognizes this factor as a foreign object and attacks it. As a result, the factor is unable to form the clot to stop the bleeding. An inhibitor is usually first noticed when a bleeding episode continues to get worse despite timely and proper infusions of factor.

Making things more challenging is the fact that everybody’s immune system functions differently. One person may respond better to a particular treatment, while another may reject the treatment entirely. Consequently, everyone who has an inhibitor needs an individualized management program — there is no “one size fits all” solution. Therefore, it is vital that a patient with an inhibitor be under the care of a physician who has experience treating these specific types of hemophilia complications. Physicians and nurses at hemophilia treatment centers (HTCs) are probably the most experienced with treatment options for you or your child. Please be cautious of others who claim to be experts in this area and have little or no experience in an HTC. You should also not rely on the advice of another patient who has an inhibitor, unless he or she is referring you to an experienced professional with extensive HTC experience. Such a patient only knows about his own inhibitor management and, as stated above, everyone’s immune system has a different response to treatments.

Up to 20 to 30 percent of severe factor VIII and 1 to 6 percent of severe factor IX patients develop an inhibitor to clotting factor at some point in their life. An inhibitor doesn’t change the number or type of bleeds that occur; it only makes the management of bleeding episodes more difficult.

Fast Facts

Inhibitors usually develop during childhood.
Inhibitors are diagnosed when there is an inadequate response to factor therapy (i.e., when the usual dose of clotting factor does not stop a bleeding episode).
An inhibitor is measured in Bethesda Units (BUs) — a measure of inhibitor activity.
The chance of developing an inhibitor is higher in patients who have a family member with an inhibitor.
Inhibitors are found in a higher percentage of African-American patients.