Factor V activity (1:20)

This test measures the activity of coagulation factor V, a protein that helps your blood form a stable clot. In the laboratory, your plasma is mixed with reagents that highlight how well factor V functions in the clotting pathway, using a fixed dilution so results are comparable.

The result reflects functional activity, not just the amount of the protein in blood. It is different from genetic testing for Factor V Leiden, which looks for a specific DNA change linked to clotting risk.

Clinicians order this test when there is unexplained bleeding, easy bruising, or abnormal screening tests such as PT or aPTT, to pinpoint whether a specific clotting factor is reduced. Low factor V activity can be seen with rare inherited factor V deficiency, in advanced liver disease where clotting proteins are produced poorly, or in conditions where clotting factors are being consumed, such as disseminated intravascular coagulation.

Because factor V is not vitamin K dependent, its activity can help distinguish vitamin K related problems or effects of certain medicines from reduced liver production. It may also be used to assess response to plasma replacement in people known to have factor V deficiency before procedures or surgery.

Your result is interpreted alongside your symptoms and other tests. A lower than expected activity suggests reduced factor V function or amount, which may be inherited or acquired.

Your care team may recommend additional studies, such as mixing studies, fibrinogen, platelet count, and liver tests, to identify the cause and guide treatment. A higher than expected activity is usually not clinically significant by itself.

This test does not diagnose Factor V Leiden, which requires a separate genetic test. If your value is outside the expected range, your clinician will review possible causes, any medicines that could interfere with testing, and whether repeat testing or treatment is appropriate.