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Factor VII assay
Definition
Factor VII assay is a blood test to measure the activity of factor VII -- one of the substances needed for coagulation (blood clotting).
Why the Test is Performed
This test is used to detect the specific cause of excessive bleeding (decreased blood clotting).
How the Test is Performed
Blood is drawn from a vein, usually from the inside of the elbow or the back of the hand. The puncture site is cleaned with antiseptic. An elastic band is placed around the upper arm to apply pressure and cause the vein to swell with blood.
A needle is inserted into the vein, and the blood is collected in an air-tight vial or a syringe. During the procedure, the band is removed to restore circulation. 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, the area is cleansed with antiseptic and punctured with a sharp needle or a lancet. The blood may be collected in a pipette (small glass tube), on a slide, onto a test strip, or into a small container. A bandage may be applied to the puncture site if there is any bleeding.
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.
Risks
- 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.
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 VII is a coagulation factor.) Each factor's reaction triggers the next reaction. The final product of the coagulation cascade is the blood clot.
Normal Results
The normal value is 50-200% of the laboratory control or reference value.
What Abnormal Results Mean
Decreased factor VII activity may be associated with:
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