SIMULTANEOUS APPEARANCE OF FACTOR (F) IX INHIBITOR DEVELOPMENT AND ANAPHYLAXIS FOLLOWING INFUSION OF FIX CONCENTRATES IN CHILDREN WITH SEVERE HEMOPHILIA (H) B. |[dagger]| 964

FIX inhibitor antibodies (IA) develop in approximately 1-2% of children with severe H B. We have recently seen two unrelated children with HB who developed anaphylaxis or severe anaphylactoid reactions when infused with plasma-derived high purity FIX. In both (ages 9 and 11 months), a FIX IA was first detected at the same time as the first severe allergic reaction.