Background: The development of inhibitors is a serious complication of coagulation factor IX (FIX) replacement therapy in patients with hemophilia B (HB), occurring in approximately 1.5-3% in HB. Currently, only less than 200 HB patients with inhibitors were reported all over world.

Aims: This study aimed to describe clinical characteristics of HB patients with inhibitors registered all over China.

Methods: Patient information was collected from the National Hemophilia Registration System in China from the year 2011 to 2021. Detailed data were also acquired by telephone follow-up on each patient.

Results: A total of 19 HB patients（16 had severe and 3 had moderate HB） with inhibitors were included in this study. The median age at diagnosis of FIX inhibitors was 10 (range, 2-43) years, and four patients had a family history of HB. Seventeen patients developed high-titer inhibitor, and the other two had low-titer inhibitor. Eleven (57.9%) patients used to be allergic to FIX products, while most (10 patients) had mild allergic reactions, such as itching and urticaria. Only one patient had dyspnea and chill. After the diagnosis of inhibitors, seven of the 19 patients underwent immune tolerance induction (ITI). The median age at the initiation of ITI was 7 (range, 2-14) years.  Three (42.9%) patients achieved a continuous negative titer successfully, and another two (28.6%) patients developed nephrotic syndrome during ITI. In those 16 patients who didn’t do or had a failure of ITI, seven patients switched to rFVIIa for bypass treatment, six patients combined PCC and rFVIIa, and three patients still used PCC for bleeding control.

Conclusions: We described the clinical features of HB patients with inhibitors in China retrospectively. The development of inhibitors in HB is related to allergic reactions/anaphylaxis, and ITI is more difficult in HB.

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ISTH Congress Abstracts - https://abstracts.isth.org/abstract/patients-with-hemophilia-b-with-inhibitors-in-china/