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Factor VIII assay

Definition

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

Alternative Names

Plasma factor VIII antigen

How the Test is Performed

How to prepare for the test

How the Test will Feel

Why the Test is Performed

Normal Results

A normal value is 50 - 200% of the laboratory control or reference value.

Normal value ranges may vary slightly among different laboratories. Talk to your doctor about the meaning of your specific test results.

The examples above show the common measurements for results for these tests. Some laboratories use different measurements or may test different specimens.

What Abnormal Results Mean

Decreased levels may be due to:

Increased levels may be due to:

  • Advanced age
  • Diabetes
  • Liver disease
  • Inflammation
  • Pregnancy
  • Obesity

Risks

Veins and arteries vary in size so it may be harder to take a blood sample from one person than another.

Other slight risks from having blood drawn may include:

  • Excessive bleeding
  • Fainting or feeling light-headed
  • Hematoma (blood accumulating under the skin)
  • Infection (a slight risk any time the skin is broken)

This test is most often done on people who have bleeding problems. The risk of too much bleeding is slightly greater for people with bleeding problems than others.

Considerations

When you bleed, the body starts a series of activities that help the blood clot. This is called the coagulation cascade. The process involves special proteins called coagulation factors (factor VIII is a coagulation factor).

Each factor's reaction triggers the next reaction. The final product of the coagulation cascade is the blood clot. Blood clots may not form normally if any one of the clotting factors is abnormally low.

References

Carcao M, Moorehead P, Lillicrap D. Hemophelia A and B. In: Hoffman R, Benz EJ Jr, Silberstein LE, Heslop HE, Weitz JI, eds. Hematology: Basic Principles and Practice. 6th ed. Philadelphia, PA: Saunders Elsevier; 2012:chap 137.

Ragni M. Hemorrhagic disorders: Coagulation factor deficiencies. In: Goldman L, Schafer AI, eds. Goldman's Cecil Medicine. 24th ed. Philadelphia, PA: Saunders Elsevier; 2011:chap 177.


Review Date: 3/3/2013
Reviewed By: Yi-Bin Chen, MD, Leukemia/Bone Marrow Transplant Program, Massachusetts General Hospital. Also reviewed by A.D.A.M. Health Solutions, Ebix, Inc., Editorial Team: David Zieve, MD, MHA, Bethanne Black, Stephanie Slon, and Nissi Wang.
The information provided herein should not be used during any medical emergency or for the diagnosis or treatment of any medical condition. A licensed medical professional 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. © 1997- A.D.A.M., Inc. Any duplication or distribution of the information contained herein is strictly prohibited.
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