Factor VII assay

Definition

The factor VII assay is a blood test to measure the activity of factor VII. This is one of the proteins in the body that helps the blood clot.

Alternative Names

Stable factor; Proconvertin; Autoprothrombin I

How the Test is Performed

A blood sample is needed.

How to Prepare for the Test

You may need to temporarily 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 is used to find the cause of abnormal bleeding (decreased blood clotting). This decreased clotting may be caused by an abnormally low level of factor VII.

Normal Results

The 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 VII activity may be related to:

• Factor VII deficiency (a bleeding disorder that affects the ability of blood to clot)
• Disorder in which the proteins that control blood clotting become over active (disseminated intravascular coagulation)
• Fat malabsorption (not absorbing enough fat from your diet)
• Liver disease (such as cirrhosis)
• 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 done on people who have bleeding problems. The risk of excessive bleeding is slightly greater than for people without bleeding problems.

References

Chernecky CC, Berger BJ. Factor VII (stable factor, proconvertin, autoprothrombin I) - blood. In: Chernecky CC, Berger BJ, eds. Laboratory Tests and Diagnostic Procedures. 6th ed. St Louis, MO: Elsevier Saunders; 2013:503-504.

Pai M. Laboratory evaluation of hemostatic and thrombotic disorders. In: Hoffman R, Benz EJ, Silberstein LE, et al, eds. Hematology: Basic Principles and Practice. 7th ed. Philadelphia, PA: Elsevier; 2018:chap 129.