Fletcher factor deficiency, source of variations of the activated partial thromboplastin time test.

The activated partial thromboplastin time test measures the integrity of the intrinsic clotting system. The sensitivity of this test to Fletcher factor deficiency is dependent upon the particular protocol and reagents utilized in the test system. The case report presented here demonstrates conflicting laboratory results obtained for a patient who had Fletcher factor deficiency, the results depending on the laboratory choice of test reagents. This serves to emphasize the importance of physician awareness of the procedures utilized in laboratory testing.