Association of factor expression levels with health-related quality of life and direct medical costs for people with haemophilia B

Aims Gene therapy trials aim to provide a functional cure for patients with haemophilia B (HB), and treatment impact is analyzed by factor IX expression levels (FELs). We investigated the relationship of FELs with health-related quality of life (HRQoL) and costs. Materials and methods This was a retrospective cross-sectional analysis of the European (CHESS I-II) and US (CHESS-US) CHESS population studies. Physicians recruited consecutive patients and extracted information from the medical records; patients completed questionnaires between 2014 and 2015 (CHESS-I), 2018-2019 (CHESS-II) and 2019 (CHESS US). Patients with inhibitors were excluded. HRQoL was assessed using the EQ-5D-5L. Twelve-month haemophilia-related direct medical costs included office visits and hospitalizations based on country-level unit costs. A Tobit model was used to analyze FELs and HRQoL and generalized linear models for direct medical costs. Results A total of 191 men with HB completed the EQ-5D questionnaire; the mean age was 36.8 years, with a mean FEL of 10.1 IU/dL (median, 4.0). Mean EQ-5D was 0.77 (SD, 0.23). The Tobit model adjusting for age, body mass index and blood-borne viruses showed every 1% increase in FEL was associated with +0.006 points in the mean EQ-5D score (p = .003). Mean haemophilia-related direct medical costs excluding factor replacement therapy were euro2,028/year (median, euro919) in CHESS I-II (EU, n = 226), and $7,171/year (median, $586) in CHESS US (n = 181). Adjusted EU and US models showed every 1% increase in FEL was associated with a decrease in haemophilia-related direct medical costs of euro108/year and $529/year, respectively. Limitations Direct medical costs were based on physician extraction of encounters from medical records, potentially underestimating costs of care. The voluntary nature of participation may have introduced selection biases. Conclusions We observed a significant association of increases in FEL with increased HRQoL and decreased costs in Europe and the United States among men with HB and no inhibitors.