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Factor IX assay
Definition Factor IX assay is a blood test that measures the activity of factor IX -- one of the substances involved in coagulation (blood clotting). Alternative Names Christmas factor assay; Serum factor IX How the test is performed Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood. A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. In infants or young children, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding. 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. Veins and arteries vary in size from one patient to another and from one side of the body to the other. Obtaining a blood sample from some people may be more difficult than from others. Why the test is performed This test is used to detect the specific cause of too much bleeding (decreased blood clotting). Normal Values A normal value is 50-200% of the laboratory control or reference value. What abnormal results mean Decreased factor IX activity may indicate: - Congenital deficiency of factor IX (hemophilia B)
- Disseminated intravascular coagulation (DIC)
- Fat malabsorption
- Liver disease (such as cirrhosis)
- Vitamin K deficiency
- Warfarin administration
What the risks are - Excessive bleeding
- Fainting or feeling light-headed
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
- Multiple punctures to locate veins
This test is most often performed on people who have bleeding problems. The risk of excessive bleeding is slightly greater than for people without bleeding problems. Special considerations When you bleed, the body launches a series of activities that help the blood clot. This is called the coagulation cascade. The process involves special proteins called coagulation factors. Each factor's reaction triggers the next reaction. The final product of the coagulation cascade is the blood clot. References Schmaier AH, Thornburg CD, Pipe SW. Coagulation and Fibrinolysis. In: McPherson RA and Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 21st ed. Philadelphia, Pa.: W.B. Saunders; 2006. Hoffman R, Benz Jr. EJ, Shattil SJ, et al., eds. Hematology: Basic Principles and Practice. 4th ed. Philladelphia, Pa: Churchill Livingston; 2005:1936-37. Review date: 2/26/2007 Reviewed By: William Matsui, MD, Assistant Professor of Oncology, Division of Hematologic Malignancies, The Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins, Baltimore, MD. Review provided by VeriMed Healthcare Network.
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