Factor VIII Activity measures the functional activity of clotting factor VIII, a critical protein in the blood coagulation cascade. This test is essential for diagnosing hemophilia A, the most common inherited bleeding disorder, and evaluating unexplained bleeding problems. Factor VIII works together with von Willebrand factor to initiate the intrinsic pathway of blood clotting. Deficiency results in prolonged bleeding times, spontaneous joint and muscle bleeding, and excessive bleeding after trauma or surgery. The test helps determine the severity of hemophilia A and guides treatment decisions, including the need for factor VIII replacement therapy. Factor VIII levels can also be elevated in inflammatory conditions, pregnancy, and certain diseases, which may increase the risk of blood clots. This test is particularly valuable for evaluating patients with unexplained bleeding, monitoring hemophilia treatment, and assessing coagulation function before surgery.