Factor IX assay - Overview

Alternative Names

Christmas factor assay; Serum factor IX

Definition of Factor IX assay:

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

How the test is performed:

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

How to prepare for the test:

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

How the test will feel:

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.

Why the test is performed:

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.

Reviewed last on: 2/28/2011
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.

References

Kessler C. Hemorrhagic disorders: Coagulation factor deficiencies. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier; 2007:chap 180.

Ragni MV, Kessler CM, Lozier JN. Clinical aspects and therapy for hemophilia. In: Hoffman R, Benz EJ Jr., Shattil SJ, et al, eds. Hoffman Hematology: Principles and Practice. 5th ed. Philadelphia, Pa: Churchill Livingstone Elsevier; 2008:chap 125.

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