title: Prevalence of factor IX inhibitors among patients with haemophilia B: results of a large-scale North American survey.
abstract: This survey provides new information on the severity of factor IX deficiencies among patients being treated for haemophilia B and on the prevalence of factor IX inhibitors in this population. A questionnaire was sent to 150 haemophilia treatment centres in the United States and Canada. 82 centres responded and provided data on 1967 patients with haemophilia B. 37% of these patients had severe haemophilia B (<1% of the normal level of factor IX), 33% had moderate haemophilia B (1-5% of the normal level of factor IX), and 30% had mild haemophilia B (>5% of the normal level of factor IX). Only 29 (1.5%) of the patients had factor IX inhibitors; 28 of these patients (96.6%) had severe haemophilia B, and one of these patients (3.4%) had moderate haemophilia B. Factor IX inhibitor titres were 0.6-1 Bethesda unit (BU) in seven patients, > 1-5 BU in four patients, > 5-10 BU in one patient, and > 10 BU in 17 patients. Factor IX inhibitors are much less common in patients with haemophilia B than in patients with haemophilia A.
authors.affiliation: University of California, Irvine, California, and Department of Pediatrics, UCI Medical Center, Orange, California, USA Jacob Katz, UCI Medical Center, 101 City Drive South, Building 27, No. 4482, Orange, CA 92668, USA.*
authors.forename: J
authors.initials: J
authors.lastname: Katz
keywords: Bethesda units; United States; factor IX; haemophilia B; inhibitor; survey