Factor XI Functional is a blood test that measures the activity of Factor XI, a protein involved in the blood coagulation cascade. Factor XI plays a role in the intrinsic pathway of blood clotting, helping to activate other clotting factors that ultimately lead to the formation of a blood clot.

This test is used to diagnose Factor XI deficiency, a condition that can lead to excessive bleeding or delayed clotting. Individuals with Factor XI deficiency may have a bleeding tendency, especially after surgery or trauma. The test is particularly important in evaluating patients with unexplained bleeding disorders or to monitor the effectiveness of certain treatments for clotting disorders.