The incidence of factor VIII inhibitors in patients with severe hemophilia A.

1. Many factors must be considered when retrospective studies are compared, for the intensity of F.VIII treatment and the frequency of inhibitor evaluation have a marked effect on inhibitor incidence. 2. The incidence of F.VIII inhibitors in patients treated with cryoprecipitate and/or intermediate purity concentrates varies greatly in different studies, with cumulative risks of 7-32% after 10-15 years of follow-up. 3. The rate of inhibitor development appears to be higher for patients treated with recombinant F.VIII, but the cumulative incidence is not greater. This may change, however, when there has been an equivalent follow-up period for the patients receiving recombinant F.VIII. 4. Cumulative risk figures may inappropriately overstate the magnitude of the problem since some inhibitors disappear after short periods of time. 5. Only prospective, long-term studies will provide more satisfactory incidence and prevalence data.