OBJECTIVETo screen for factor VIII inhibitor in patients with hemophilia A (HA) and explore the environmental risk factors for inhibitor development.

METHODSTotally 265 patients with HA were enrolled, including 107 consecutive inpatients and outpatients in Peking Union Medical College Hospital from April 2003 to April 2007 and 158 patients newly recruited from other hospitals. FVIII: C activity was measured by one-stage coagulation assay. FVIII inhibitor was determined using Bethesda method.

RESULTSIn 265 HA patients, FVIII inhibitor was detected in 22 patients (8.3%). Nine of them (86.4%) were low responders (inhibitor titers < or = 5 000 BU/L), 3 (13.6%) were high responders (the titers > 5 000 BU/L). The frequency of FVIII inhibitor was 50% in the patients aged over 50 years, which was significantly higher than those in other age groups (P = 0. 000). Among 158 newly recruited patients with full clinical data, the frequency of FVIII inhibitor was 12.8% in patients who had received infusion of FVIII products for more than 12 doses on average each year, while it was 5.8% in whom the infusion doses were less than 12 (P = 0.156). The frequency of FVIII inhibitor was 28.5% in patients with a history of continuous infusion of FVIII products whereas it was only 1.6% in patients without such history (P = 0.000). In patients who exposed to multiple-branded or single-branded FVIII products, the frequencies of FVIII inhibitor were 9.3% and 3.9%, respectively (P = 0.229).

CONCLUSIONThe development of factor VIII inhibitor in patients with hemophilia A may be related to the age and the history of continuous infusion of FVIII products.