Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (916 page)

   F5 gene mutations, other than R506Q, are not evaluated by this assay.

FACTOR VIII (ANTIHEMOPHILIC FACTOR)
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   Definition

   Factor VIII is synthesized in the liver and endothelial cells of other organs, including the spleen, which plays an important role in the synthesis of factor VIII. It is unaffected by liver failure or vitamin K deficiency.

   It is the principal cofactor in the intrinsic pathway of coagulation and serves as a substrate for proteolysis by the proteins C/protein S complex.

   PT (INR) is not affected by deficiency of factor VIII.

   Most laboratories use a specific coagulant assay to measure factor VIII.

   Chromogenic assays are also available.

   Immunologic assays determine factor VIII antigen. The antigen is concordant to activity in most cases but may be normal occasionally in patients with a functional defect in the molecule.

   
Normal range:
70–150%.

   Use

   Purified or recombinant factor VIII is used therapeutically for patients with hemophilia A.

   Immunologic assays for factor VIII may be useful in the diagnosis of von Willebrand disease but are not necessary in the diagnosis of most cases of hemophilia.

   Interpretation