Factor VIII Activity LabCorp

The Factor VIII Activity test is used in the evaluation of an isolated, prolonged aPTT. Diagnosis of hemophilia A and as an aid in the diagnosis of von Willebrand factor (vWF) deficiency. 

Factor VIII is an acute phase reactant and can be elevated in a multitude of clinical conditions, which can affect the accuracy of the test in diagnosing hemophilia. Factor VIII levels should not be used to determine the carrier status of females and genetic testing should be utilized for this purpose. Factor VIII inhibitors (both autoantibodies that develop after replacement therapy and autoantibodies that develop spontaneously) can result in low factor VIII levels. A lupus anticoagulant may also cause factor VIII activity to appear spuriously low and chromogenic factor VIII activity is recommended in this circumstance. Direct Xa or thrombin inhibitor therapy may cause factitiously low results. 

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