Factor II Activity (1:20)

The Factor II 1:20 test measures the functional activity of prothrombin (also called Factor II), a clotting protein produced by your liver with the help of vitamin K. Your plasma is diluted and tested in a clot-based system to see how well Factor II participates in forming a stable clot.

Results are reported as activity in units per milliliter relative to normal plasma. This test is often performed along with screening tests such as PT and aPTT or with other specific factor assays to understand where a clotting problem may be occurring.

Too little Factor II activity can lead to easy bruising, nosebleeds, heavy menstrual bleeding, or bleeding after injuries or procedures. Low activity may be inherited or acquired, such as from vitamin K deficiency, liver disease, certain autoimmune conditions, or medicines that reduce the production or function of clotting proteins.

Your clinician may order this test when screening tests are abnormal, when there is unexplained bleeding, before surgery in someone with bleeding symptoms, or when an inhibitor against Factor II is suspected. It can also help assess the impact of vitamin K antagonist therapy and guide treatment of reversible causes like vitamin K deficiency.

If your Factor II activity is lower than expected, your clinician will interpret it together with PT, aPTT, mixing studies, and other factor levels to decide whether the cause is a deficiency or an inhibitor. They may review your medicines, check vitamin K status, and evaluate liver function, since these can strongly affect Factor II.

Higher than expected activity is less common and is usually interpreted in the context of your clinical history, medicines, and hormonal status. Follow-up may include repeat confirmation, treatment of reversible causes, or referral to a specialist for further evaluation, including genetic testing if a rare inherited disorder is suspected.