The blood coagulation factors are proteins in blood plasma that produce an orderly clot at a site of injury or surgical incision. Deficiencies in the amount or function of either factor VIII or IX can result in severe hemorrhage either spontaneously, or even after trivial trauma. Bleeding may also occur into vital areas, such as the brain or gastrointestinal tract. Even mild hemophilia can produce hemorrhage after minimally invasive procedures, like the injection of anesthetic for dental procedures. Major trauma or surgery can result in life-threatening hemorrhage if not treated appropriately.
Joint replacement is a frequent indication for surgery in adult patients with hemophilia.
A clinical laboratory measures the amount of factor VIII or IX in plasma, which is expressed as a percentage of the activity of the factor in normal plasma. The normal range of factor activity is approximately 50 to 150 percent. Mild hemophilia is an activity of the factor from 5 to 50 percent, moderate from 1 to less than 5 percent, and severe hemophilia is less than 1 percent. While the aPTT is an excellent test for screening for deficiency states, it is not precise enough to follow the efficacy of therapy or to make an accurate diagnosis. The prothrombin time, or PT, is another normal screening test of blood coagulation in hemophilia.