Hemophilia B is less common than Hemophilia A. It is also known as Factor IX(9) Deficiency or “Christmas disease,” named after the first patient described to have the disease. A person with hemophilia B has a deficiency of factor IX(9) clotting protein in their blood, thus they have a hard time forming clots to stop bleeding. There are three different levels of hemophilia B: severe, moderate and mild. A person with severe hemophilia B has less than 1% of factor IX in their blood. Factor IX(9) replacement is needed several times a month to prevent bleeding. Bleeding can be caused by injury or complications. A person with moderate hemophilia B has 1% to 5% of factor IX in their blood. Bleeds in a person with moderate hemophilia are commonly caused by injury, surgery or dental work. A person with mild hemophilia B has 6% to 50% of factor IX(9) in their blood. A person with mild hemophilia B will have fewer bleeds than a person with moderate or severe hemophilia B. Mild bleeds are usually caused by injury, surgery, or dental work.