Factor X assay
The factor X assay is a blood test to measure the activity of factor X. This is one of the proteins in the body that helps the blood clot.
How the Test is Performed
A blood sample is needed.
How to Prepare for the Test
You may need to stop taking some medicines before this test. Your health care provider will tell you which ones.
How the Test will Feel
When the needle is inserted to draw blood, some people feel moderate pain. Others feel only a prick or stinging. Afterward, there may be some throbbing or slight bruising. This soon goes away.
Why the Test is Performed
This test may be used to find the cause of excessive bleeding (decreased blood clotting). The decreased clotting may be caused by an abnormally low level of factor X.
A normal value is 50% to 200% of the laboratory control or reference value.
Normal value ranges may vary slightly among different laboratories. Some labs use different measurements or may test different samples. Talk to your provider about the meaning of your specific test results.
What Abnormal Results Mean
Decreased factor X activity may be related to:
- Disorder in which abnormal proteins build up in tissues and organs (amyloidosis)
- Factor X deficiency (a bleeding disorder caused by a lack of blood clotting factor X)
- Disorder in which the proteins that control blood clotting become over active (disseminated intravascular coagulation)
- Fat malabsorption (not absorbing enough fat from your diet)
- Heparin use
- Liver disease
- Vitamin K deficiency
- Taking blood thinners
There is little risk involved with having your blood taken. Veins and arteries vary in size from one person 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.
Other risks associated with having blood drawn are slight, but may include:
- Excessive bleeding
- Fainting or feeling lightheaded
- Multiple punctures to locate veins
- Hematoma (blood accumulating under the skin)
- Infection (a slight risk any time the skin is broken)
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.
Chernecky CC, Berger BJ. Factor X (Stuart-Prower factor) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:506-507.
Gailani D, Wheeler AP, Neff AT. Rare coagulation factor deficiencies. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 137.
Ragni MV. Hemorrhagic disorders: coagulation factor deficiencies. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 165.
Last reviewed on: 1/19/2021
Reviewed by: Todd Gersten, MD, Hematology/Oncology, Florida Cancer Specialists & Research Institute, Wellington, FL. Review provided by VeriMed Healthcare Network. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.