The factor VIII assay is a blood test that measures the activity of factor VIII — one of the substances involved in blood clotting (coagulation).
Plasma factor VIII antigen
How the test is performed
A blood sample is needed. For information on how this is done, see:
How to prepare for the test
No special preparation is needed for this test.
How the test will feel
When the needle is inserted to draw blood, some people feel moderate pain, while others feel only a prick or stinging sensation. Afterward, there may be some throbbing.
Why the test is performed
This test is used to find the cause of too much bleeding (decreased blood clotting), or if a family member is known to have
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:
Disseminated intravascular coagulation(DIC)
- Presence of a Factor VIII inhibitor (antibody)
Von Willebrand’s disease
Increased levels may be due to:
What the risks are
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.
Other risks associated with having blood drawn are slight but 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 performed on people who have bleeding problems. The risk of excessive bleeding is slightly greater for people with bleeding problems than for people without bleeding problems.
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 VIII is a coagulation factor).
Each factor’s reaction triggers the next reaction. The final product of the coagulation cascade is the