The factor VIII assay is a blood test that measures the activity of factor VIII -- one of the substances involved in blood clotting (coagulation).

Plasma factor VIII antigen

A blood sample is needed. For information on how this is done, see: Venipuncture

No special preparation is needed for this test.

When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.

This test is used to find the cause of too much bleeding (decreased blood clotting), or if a family member is known to have hemophilia A. The test may also be done to see how well treatment for hemophilia A is working.

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Factor VIII assay Results

Review Date: 02/28/2011
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine; and Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)