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

Christmas factor assay; Serum factor IX

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

The health care provider may advise you to stop taking drugs that may affect the test.

When the needle is inserted to draw blood, you may feel moderate pain, or 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 B. The test may also be done to see how well treatment for hemophilia B is working.

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Factor IX 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)