Frequent but low titre factor VIII inhibitors in haemophilia A patients treated with high purity concentrates.

The development of inhibitor antibodies is one of the more important complications in the management of haemophilia patients. In a previous study, the prevalence of inhibitor varies between 5 and 52%, seems to be different for different types of concentrates, and is less frequent in multitransfused patients. In our prospective study we followed for 3 years 62 multitransfused haemophilia patients without inhibitor or past history of inhibitor. Thirty-seven haemophilia patients were treated with intermediate purity factor VIII concentrates, whereas 25 were given high purity concentrates (from the eighth month of the study five of these patients were treated with recombinant products). Factor VIII inhibitor antibody developed in seven of 25 haemophilia patients treated with high purity concentrates or recombinant products, whereas none of the haemophilia patients treated with intermediate purity concentrates had inhibitors. The difference was statistically significant (P < 0.001; OR = 0.06, 95% CI 0.001-0.3). In all patients, the titre of the inhibitor was low and no problem occurred in their management. Since inhibitors appeared in multitransfused patients when transfused with high purity concentrates and/or when the patients were switched to recombinant FVIII product, the development of inhibitor seems to be due to the administration of a new concentrate. Therefore this potential complication must be considered every time a new concentrate is administered.