Factor VIII assay
Alternate Names : Plasma factor VIII antigen
Definition
The factor VIII assay is a blood test that measures the activity of factor VIII -- one of the substances involved in blood clotting (coagulation).
Why is the Test Performed?
Your doctor may order this test if you have signs of easy bruising or bleeding, such as hemophilia. The test may also be done to see how well treatment for hemophilia is working.
How is the Test Performed?
Blood is typically drawn from a vein, usually from the inside of the elbow or the back of the hand. The area is cleaned with germ-killing medicine (antiseptic). The health care provider wraps an elastic band around the upper arm to apply pressure to the area and make the vein swell with blood.
Next, the health care provider gently inserts a needle into the vein. The blood collects into an airtight vial or tube attached to the needle. The elastic band is removed from your arm. Once the blood has been collected, the needle is removed, and the puncture site is covered to stop any bleeding. In infants or young children, a sharp tool called a lancet may be used to puncture the skin and make it bleed. The blood collects into a small glass tube called a pipette, or onto a slide or test strip. A bandage may be placed over the area if there is any bleeding.
How to Prepare for the Test?
No special preparation is necessary for this test.
How will the Test 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.
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