Skip to Main Content
factor-x-assay-708x556-2x
Medical Tests A-Z

Factor X assay

Definition

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.

Alternative Names

Stuart-Prower factor

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.

Normal Results

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 overactive (disseminated intravascular coagulation)
  • Fat malabsorption (not absorbing enough fat from your diet)
  • Heparin use
  • Liver disease
  • Vitamin K deficiency
  • Taking blood thinners

Risks

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.

References

Gailani D, Benjamin FT, Wheeler AP. Rare coagulation factor deficiencies. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 8th ed. Philadelphia, PA: Elsevier; 2023:chap 135.

Ragni MV. Hemorrhagic disorders: coagulation factor deficiencies. In: Goldman L, Schafer AI, eds. Goldman-Cecil Medicine. 26th ed. Philadelphia, PA: Elsevier; 2020:chap 165.

Sarode R, Kessler CM. Coagulation and fibrinolysis. In: McPherson RA, Pincus MR, eds. Henry's Clinical Diagnosis and Management by Laboratory Methods. 24th ed. Philadelphia, PA: Elsevier; 2022:chap 40.

Review Date: 02/02/2023

The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed physician should be consulted for diagnosis and treatment of any and all medical conditions. Call 911 for all medical emergencies. Links to other sites are provided for information only -- they do not constitute endorsements of those other sites. Copyright ©2019 A.D.A.M., Inc., as modified by University of California San Francisco. Any duplication or distribution of the information contained herein is strictly prohibited.

Information developed by A.D.A.M., Inc. regarding tests and test results may not directly correspond with information provided by UCSF Health. Please discuss with your doctor any questions or concerns you may have.

Share