Coagulation factor inhibitors

Test based on the inability of normal plasma (in a 50:50 mixture) to correct prolonged APTT (or PT) of patient (test) plasma.

Further tests to identify and quantitate inhibitor are based on coagulation factor assays.

Factor VIII inhibitors develop in <10% of patients with haemophilia A; rarely in patients with autoimmune disease, lymphoproliferative disorders and other malignancies; in the post-partum period and in otherwise normal individuals.

Factor IX inhibitors develop in <2% of patients with haemophilia B and are very rare in other disorders.

Other specific coagulation factor inhibitors are extremely rare, but may develop (particularly in the elderly). Otherwise normal (non-haemophilic) patients who develop an inhibitor may present with acute bleeding.

Inhibitors may be low or high titre; low titre inhibitors do not cause major therapeutic problems and may become undetectable over time, even with continued coagulation factor replacement therapy. High titre inhibitors pose a major therapeutic problem; for factor VIII inhibitors the degree of cross reactivity with porcine factor VIII should be documented as a guide to whether this product, if available, can be used for replacement therapy.