Testing for Inhibitors

Hemophilia Treatment Centers test people with hemophilia for inhibitors every six to twelve months.  This routine screening is part of the comprehensive exam.  Inhibitors are measured in "Bethesda units".  The higher the number of units, the harder it will be to stop bleeding.  Anytime you do not stop bleeding after taking your usual dose of factor, you should be tested for an inhibitor.  You should also be tested for an inhibitor before having surgery.

If you have an inhibitor, you must be followed closely by your hemophilia center.  Checks of the inhibitor level should be done every three to six months or as often as your doctor says.  Your medical alert tag and I.D. card should note that you have an inhibitor.

High and low inhibitor response levels

People with hemophilia can have different inhibitor levels.  Generally, people with inhibitors are said to have a high or low response.  A person with a high or strong inhibitor response will have a strong antibody response after taking factor.  His inhibitor level can remain high enough to destroy factor for a long time after taking it.  Although the inhibitor level may fall after some time, it can go back up when he takes factor again.  This is known as a memory response.

In someone with a low or weak inhibitor response, less factor is destroyed before it is involved in clotting.  The inhibitor level of a low responder stays low, even with repeated factor treatments. About 80% of people with inhibitors are high responders and 20% are low responders.  A person may start out as a low responder and become a high responder.  The level of inhibitor response does not seem to be genetic (inherited).  People with hemophilia in the same family can have different inhibitor responses. In some cases inhibitors disappear.  They may not reappear, even if the people continue to use factor.  This happens more often in low responders than in high responders.