Investigating the Relationship between Endogenous Factor VIII Levels and Annual Bleed Rates and Health-Related Quality of Life in Patients with Hemophilia a Not Treated with Factor VIII Prophylaxis
Authors: Jones Cheryl , Wu Yunchou , Kragh Nana , Bystrická Linda , Wilson Amanda , Burke Tom 
Published: December 2023

Background
Haemophilia A (HA) is a rare genetic disorder characterized by excessive bleeding caused by dysfunctional or absent clotting factor VIII (FVIII). Levels of FVIII determine severity of HA; 5% to &lt;40% of normal FVIII levels is classified as mild disease, 1-5% is moderate, and &lt;1% is severe.
Current standard of care for severe hemophilia A is prophylaxis, with FVIII replacement keeping levels above 3-5% to prevent bleeding episodes. Less severe patients, or patients who opt-out of prophylaxis, may be treated on-demand. In patients not on prophylaxis, factor levels (FLs) are considered endogenous.
Aims
The purpose of the study was to explore the relationship between endogenous FLs and ABR; and FLs and Health-Related Quality of Life (HRQoL), in patients across all severities treated on-demand.
Methods
The analysis was conducted using the CHESS II dataset - a retrospective, cross-sectional study conducted in Denmark, France, Germany, Italy, The Netherlands, Romania, Spain, and The United Kingdom [2018-19]. Physicians completed questionnaires about their patients, and patients completed HRQoL questionnaires. The inclusion criteria for this analysis was restricted to adult male patients without inhibitors or treated with prophylaxis. ABR was defined as the total number of bleeds recorded in the patient's medical records within the previous 12 months from patient enrolment. HRQoL was measured using the EQ5D-5L and valued using UK preference weights for comparison. Spearman's correlation was used to assess the relationships between FLs and both ABR and HRQoL. Regression models were used to estimate the relationships controlling for key covariates, including age, body mass index, and blood-borne viruses (HIV, Hepatitis B and C).
Results
A total of 403 patients from six countries (Italy, France, Germany, Spain, Romania, and United Kingdom) were included. Patients with mild, moderate, or severe HA accounted for 30%, 33%, and 37% of the sample, respectively. The mean age was 37.2 years with mean BMI 24.5 kg/m 2. The mean baseline FLs of all patients in the sample was 7 IU/dL (SD, 10.2) overall and 8.1 IU/dL (SD, 11.3) for the subset with HRQoL data (N = 167). The mean ABR was 2.3 bleeds/year (SD, 2.64) and the mean HRQoL score (n = 167) was 0.777 (SD, 0.197).
Correlation analyses identified statistically significant, non-linear relationships between FLs and ABR, and FLs and HRQoL. The model showed lower ABRs in patients with higher endogenous FLs (figure 1). The regression suggests that on average, for every 1% higher endogenous FLs, ABR is 3.9% [95%CI: 2.8, 5.0%] (0.09 units) lower. In other words, an increase in FLs of 11% is associated with a reduction in ABR of approximately 1 bleed per year (figure 1). For HRQoL and FLs, the regression analyses show higher HRQoL with higher FLs (figure 2). The model showed every 1% higher FLs was associated with 0.0054 [95%CI: 0.003, 0.008] points higher EQ5D scores on average; therefore, an increase in FLs of 13% could achieve a minimal clinically important difference in HRQoL. Given non-linearity of the relationship, larger gains in HRQoL may come from raising FLs in more severe patients.
Conclusion
The results of this study reflect the spectrum of patients with HA treated on-demand in Europe. Due to the selection of patients not treated with prophylaxis, some of whom may have lower bleeding phenotypes, bleed rates and HRQoL are likely underestimated. The analyses show patients with higher endogenous FLs may experience fewer bleeds and better HRQoL than patients with lower FLs. This relationship may be maintained when considering FLs during prophylactic treatment. Higher FLs are not only related to clinical benefits, but also humanistic outcomes.