Factor XI Deficiency

What is factor XI deficiency?

People with factor XI (11) deficiency, also called hemophilia C, have low levels of factor XI. Although factor XI is not as critical to clotting as other factors, a person with factor XI deficiency may still need treatment and attention. Bleeding in people with factor XI deficiency is sometimes affected by other factors or may be apparent only with surgery.

Recently, an international organization (International Society on Thrombosis and Hemostasis) proposed that FXI deficiency shows no association between the severity of the disease and the factor activity level. Therefore, there are no factor activity levels that directly correlate with mild, moderate or severe disease.

What causes it?

If either parent has factor XI deficiency, it will be passed on to their children. It can occur in both men and women. It is more common among Ashkenazi Jews (nearly 1 in every 8), but it affects non-Jewish people as well. Factor XI deficiency occurs in 1 in every million people.

What are the symptoms?

Bleeding in people with factor XI deficiency is not predictable or related specifically to the factor level. Spontaneous bleeding is very rare. However, there are common signs and symptoms, such as:

  • Bleeding after injury in the mouth or nose
  • Blood in the urine
  • Bleeding after surgery, especially tonsillectomy, sinus surgery, and dental work
  • In women, heavy menstrual bleeding and bleeding related to childbirth

How is it diagnosed?

Factor XI deficiency is diagnosed after finding screening tests that identify prolonged activated partial thromboplastin time (aPTT) then by following up to determine that factor XI activity is lower than normal. These results should be confirmed by a specialized health care provider.

How is it treated?

Treatment is necessary for traumatic bleeding, and necessary around the time of a surgery or during bleeding related to pregnancy. There are no specific factor XI concentrates in the US. Other hemostatic agents have been studied that can help the blood to clot.

Because patients may not have any factor XI in their blood, if they get administered a blood derived product containing factor XI they can develop an immune response. This response of developing antibodies (also called inhibitors) can occur in patients with severe factor XI deficiency.