Coagulation factor inhibitors

Last updated: Wednesday, 31, March, 2004

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Item Process

4.5 mL blood added to 0.5 mL citrate.


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.


Reduced clinical and/or assay response to coagulation factor replacement therapy in haemophilia A or B.

Unexplained prolongation of the APTT (or more rarely PT) in patients with recent onset of excessive bleeding; particularly in those with autoimmune disease, lymphoma or myeloma and in post-partum patients.

See also Lupus inhibitor.


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.


Brettler DB. Bailliere’s Clin Haematol 1996; 9: 319-329.

Cohen AJ and Kessler CM. Bailliere’s Clin Haematol 1996; 9: 331-354.