Definition

Factor X assay is a blood test to measure the activity of factor X -- one of the substances involved in coagulation (blood clotting).

How to prepare for the test

Your health care provider may ask you to stop taking certain medications.

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 may be used to detect the specific cause of excessive 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 X activity may indicate:

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. (Factor X is a coagulation factor.) Each factor's reaction triggers the next reaction. The final product of the coagulation cascade is the blood clot.

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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.

Lots More Information:
•Factor X deficiency
•Malabsorption
•Liver disease
•Vitamin K
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.