Hemophilia B is a deficiency of factor IX. Hemophilia B is much less common than hemophilia A, affecting about one in 25,000 to 30,000 males. Factor IX, like factor VIII, is in the intrinsic arm of the coagulation cascade. Thus, just as with hemophilia A, hemophilia B patients will have a prolonged PTT/aPTT.
When factor levels fall to very low levels (<1%) in Hemophilia A or B, patients will often be given the missing coagulation factor as a prophylactic measure to prevent spontaneous bleeding. The dosing of coagulation factors is based on the number of bleeding episodes a patient has had and their factor activity level. Physicians may prescribe factors for patients with factor VIII or IX levels that range anywhere from 1 to 40%.
The workup of hemophilia B is very similar to that of hemophilia A. The only difference being that factor IX assays are used to confirm and monitor the patient rather than factor VIII assays.
