Some patients with hemophilia A (hereditary Factor VIII deficiency) will develop Factor VIII inhibitors. These may interfere with the effectiveness of Factor VIII replacement.

A patient with an inhibitor can be classified as a low or high responder depending on

(1) the titer of the inhibitor and

(2) the change in titer with time after exposure to Factor VIII replacement



Titer of the Inhibitor

Change in Titer with Time



no rise in titer with exposure


low to high

marked rise with exposure (anamnestic response)



• For the implementation I used an intermediate category for someone who does not meet the criteria for either responder group.


A low responder can usually be treated with Factor VIII replacement without problems.


A high responder with a high titered inhibitor may be difficult to treat since any Factor VIII is inactivated by the inhibitor.

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