Hemophilia is primarily treated by replacing the absent or abnormal clotting factors in the blood. One of the major sources for clotting factors is donated blood. Prior to 1985, many people with hemophilia became infected with the human immunodeficiency virus (HIV) because they received blood products that were contaminated from infected donors. Beginning in 1985, donated blood was routinely tested and screened for HIV and other viruses, such as hepatitis B and hepatitis C.

The blood supply is now much safer because of better donor screening tests and new purification techniques that kill viruses in blood. Viruses sometimes are still spread through donated blood, but HIV and other viruses that cause chronic hepatitis are almost always detected during the careful screening process. The purification process also destroys most viruses that are not detected.

Some viruses are more difficult to detect even with careful screening. Viruses that are occasionally transmitted through blood supplies include hepatitis A, parvovirus (the virus that causes fifth disease), Epstein-Barr virus (EBV), and cytomegalovirus (CMV).

Some people develop antibodies to the injected clotting factor. These antibodies are called inhibitors, and they may make it more difficult to treat bleeding episodes. Up to 20% of children with hemophilia receiving fresh frozen plasma or cryoprecipitate clotting factor develop inhibitors.¹