HEAD‐US Score and Cartilage Biomarkers in Patients With Severe Haemophilia A Who Receive Low‐Dose Factor VIII Prophylaxis

Among patients with severe haemophilia A (PwSHA; factor VIII coagulant activity [FVIII:C] < 1 IU/dL), recurrent haemarthrosis is a common and debilitating manifestation, leading to progressive joint deterioration. If left undetected or improperly managed, irreversible haemophilic arthropathy can contribute to chronic pain, compromising quality of life (QoL) and ultimately disability in HA individuals [1]. With the advent of FVIII prophylaxis, the risk of haemarthrosis has declined significantly. However, the implementation of standard FVIII regimens can be a constraint in low-to-middle-income countries (LMICs), resulting in the adoption of low-dose FVIII protocols. Albeit offering a pragmatic solution, concerns remain regarding their long-term efficacy in joint protection [2]. To assess joint health in PwSHA, imaging modalities are routinely employed, accompanying clinical evaluations. Among these, the Haemophilia Early Arthropathy Detection with Ultrasound (HEAD-US) scoring system has gained attention due to its ability to detect early joint changes non-invasively. Elbows, knees and ankles were evaluated and scored based on synovial hypertrophy, cartilage damage and subchondral bone irregularities [3]. Despite its practicability, ultrasonography reflects cumulative structural alterations and may lack sensitivity to real-time biochemical processes occurring intraarticularly [4]. In this context, several biomarkers, for example, serum ferritin, serum C-reactive protein (CRP), erythrocyte sedimentation rate (ESR) and urinary C-terminal telopeptide of type II collagen (uCTX-II), which indicate inflammation and/or cartilage degradation, may offer promising adjuncts to imaging to detect subclinical joint deterioration in PwSHA. In particular, uCTX-II increases during early cartilage matrix breakdown and can decrease with improvement of joint stability, thus serving as a dynamic indicator of therapeutic efficacy [5]. Since evidence evaluating these surrogates in the HA population during low-dose FVIII prophylaxis remains scarce, this prospective single-centre cohort study aims to investigate changes in joint health using the HEAD-US score and associated biomarkers in PwSHA transitioning from weight-based low-dose FVIII to pharmacokinetic (PK)-guided low-dose extended half-life (EHL) FVIII prophylaxis under resource-limited circumstances in Thailand. During 2024, male PwSHA without FVIII inhibitors, aged ≥ 6 years, who received regular weight-based low-dose FVIII prophylaxis for ≥ 6 months, were enrolled. Patients with planned major surgery or human immunodeficiency virus infection were excluded. After informed consent, participants continued their existing weight-based low-dose FVIII regimens using standard half-life or EHL FVIII concentrates (10–15 IU/kg, 1–3 times/week) for 16 weeks (Phase I), then switched to PK-guided low-dose EHL FVIII prophylaxis targeting a trough FVIII:C of ≥ 1 IU/dL for another 16 weeks (Phase II; Table S1). To assess the PK profiles using a Bayesian analysis in a population PK model [2], each participant received an infusion of EHL FVIII concentrate 20 IU/kg, followed by blood sampling for one-stage clot-based FVIII:C assays at 0, 3 and 72 h post-infusion. Then, EHL FVIII dosing was optimized according to the PK curve [2]. At weeks 16 (during Phase I) and 32 (during Phase II), the HEAD-US score and biomarkers of interest, including serum ferritin, serum CRP, ESR and uCTX-II, were evaluated (Figure S1; Tables 1 and S2). Joint ultrasonography (Aplio i800 Ultrasound, Canon Medical Systems, Tochigi, Japan) was performed by a radiologist specialized in musculoskeletal imaging (N.N.). Annualized bleeding rate (ABR), annualized joint bleeding rate (AJBR), haemophilia joint health score (HJHS), and haemophilia-specific QoL score, were determined parallelly. For breakthrough bleeds, episodic EHL FVIII replacement therapy was applied as previously described [2]. This study (ClinicalTrials.gov NCT06816953) was conducted following the ethical approval at the study centre (Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand; IRB no. 0736/67). Using Stata v18.0 (StataCorp, College Station, TX), descriptive statistics were analysed. Medians with interquartile ranges (IQRs) were estimated for continuous variables, and the Wilcoxon signed-rank test was used to compare pre- and post-intervention results, considering the statistical significance at p < 0.05. Of 18 PwSHA (detailed in Table S1), 55.6% (n = 10) had at least one target joint. Before enrolment, 61.1% (n = 11) and 38.9% (n = 7) received secondary/tertiary and primary FVIII prophylaxis, respectively. Comparing Phase I to Phase II, the HEAD-US score reduced significantly in the overall cohort (median 8 [IQR 0–29] vs. 5 [IQR 0–25]; p = 0.04). Its numerical decline was conspicuous in patients with target joints (median 29 [IQR 14–38] vs. 25 [IQR 10–37]), although statistical significance did not reach. Whereas, in patients without a target joint (n = 8) whose baseline HAED-US score was naturally better (p < 0.001), its change was only subtle (Table 1). Nevertheless, in parallel, uCTX-II levels decreased significantly in Phase II across all subgroups. The medians of differences were −92.6 (IQR −147.5 to −33.3; p < 0.001), −42.7 (IQR −141.3 to −23.4; p = 0.004) and −94.2 (IQR −152.2 to −59.6; p = 0.008) ng/mmol creatinine, in the overall cohort, patients with target joints, and patients without a target joint, respectively (Table 1). These findings suggest that PK-guided low-dose EHL FVIII prophylaxis may prevent cartilage degradation and promote a possible slowing/stabilization of joint deterioration more effectively than weight-based low-dose FVIII prophylaxis in PwSHA, irrespective of preexisting joint status. In contrast, traditional inflammatory markers did not exhibit significant changes (Table 1). Serum ferritin (median 119.6 [IQR 49.5–241.3] vs. 77.4 [IQR 38.7–237.1] ng/mL), serum CRP (1.4 [IQR 0–5.7] vs. 1.9 [IQR 0–5.0] mg/dL) and ESR (8 [IQR 3–15] vs. 7 [IQR 3–8] mm/h) were statistically unchanged, reflecting their limited sensitivity to detect early amelioration of joint inflammation. Transitioning to the PK-guided low-dose EHL FVIII regimen also improved clinical bleeding and HA-related health (Table 2), despite an increase in weekly FVIII consumption for prophylaxis (p = 0.03; Table S1) [2]. In the overall cohort, ABR (p = 0.03), AJBR (p = 0.03) and HJHS (p = 0.04) decreased significantly from the medians of 2 (IQR 0–12) to 1.5 (IQR 0–2), 2 (IQR 0–10) to 0 (IQR 0–2) and 10 (IQR 0–20) to 4 (IQR 0–16), respectively. Their improvements were pronounced in patients with target joints, but not in those without a target joint whose baseline ABR (p = 0.01), AJBR (p = 0.004) and HJHS (p < 0.001) were less severe (Table 2). However, a significant reduction in QoL score was achievable in all subgroups with the median of differences of −20 (IQR −30 to −13) for all patients (p < 0.001). Consistent with the previous study [2], our results support the potential benefits of PK-guided low-dose EHL FVIII prophylaxis for PwSHA, in not only clinical but also biochemical/radiological outcomes. This before-after study demonstrates the biochemical, radiological, and clinical impacts of utilizing PK-guided low-dose EHL FVIII prophylaxis in PwSHA previously treated with weight-based low-dose FVIII prophylaxis under limited resources. Key findings include a significant reduction in uCTX-II, representing a decrease in cartilage resorption, regardless of target joint status, with a modest yet significant improvement in the HEAD-US score. These surrogates are accompanied by improved HA-related clinical parameters, synergistically confirming the benefits and feasibility of this personalized prophylactic approach for the HA population in LMICs [2]. The elevation of uCTX-II in PwSHA is reportedly associated with faster progression of haemophilic arthropathy determined by the radiograph-based Pettersson score [6]. In this study, the noteworthy decline in uCTX-II indicates a protective effect of PK-guided low-dose EHL FVIII prophylaxis against joint cartilage damage secondary to haemarthrosis, aligning with the alleviated ultrasonography-based HEAD-US score. Furthermore, since uCTX-II physiologically peaks within 3–5 days and normalizes within 12–14 days post-haemarthrosis in PwSHA [7], the reduction in uCTX-II across all subgroups likely reflects a reduced frequency of haemarthrosis, including subclinical microbleeds. This effect was notable even in patients without a target joint whose ABR, AJBR, HJHS, and the HEAD-US score were already low before the regimen transition. Conversely, the absence of significant changes in serum ferritin, serum CRP and ESR, which are systemic inflammatory markers, suggests their futility to represent a subtle improvement in intraarticular inflammation. While the HEAD-US score correlated with HJHS in PwSHA with/without regular FVIII prophylaxis and could guide clinical decision [8, 9], our findings underscore the utility of uCTX-II as a complementary biomarker to enhance comprehensive joint assessment in PwSHA receiving low-dose FVIII regimens. This study emphasizes the usefulness of personalized PK-guided low-dose EHL FVIII prophylaxis in optimizing HA therapeutic efficacy in LMICs, where standard FVIII doses remain limitedly accessible. Nonetheless, the small cohort size limits the statistical power to determine outcome differences, particularly in subgroup analyses. For biomarker results, variability of sampling time points relative to haemarthrosis, the unknown specificity of uCTX-II for affected joint cartilage and/or subclinical microbleeds in PwSHA, and nonspecific systemic release may restrict interpretation. The absence of standardized serum-/urine-based assays, age-dependent variations [10], and possible variability between commercial kits also constrain the generalizability of the uCTX-II results. The short study duration additionally precludes assessing long-term outcomes. Integrating uCTX-II with the HEAD-US score and traditional clinical evaluations as a valuable joint health monitoring system in PwSHA receiving prophylaxis with low-dose EHL FVIII, or other potential alternatives, for example, low-dose emicizumab [11], therefore warrants further investigations in larger studies with extended follow-up. In conclusion, transitioning PwSHA from conventional weight-based low-dose FVIII to PK-guided low-dose EHL FVIII prophylaxis significantly reduces cartilage degradation, reflected by the improvement in HEAD-US score and uCTX-II. Combining these non-invasive biochemical and radiological tools provides a feasible monitoring approach. Although future studies, including comparisons with healthy controls and/or athletes, are essential to validate the role of uCTX-II as an adjunct biomarker for joint health assessment in PwSHA, this PK-guided low-dose EHL FVIII regimen depicts a meaningful step toward evolving prophylactic HA care into a tailored practice in LMICs. A.P. designed the study, implemented the treatment protocol, collected and interpreted data, data analysis and wrote the manuscript draft. C.M. interpreted data, data analysis, critically reviewed and edited the manuscript. N.N. performed joint ultrasonography and assigned the HEAD-US score. D.S. designed and supervised the study, implemented the treatment protocol, collected and interpreted data, data analysis, critically reviewed and edited the manuscript. All authors revised and approved the final manuscript. This study has been supported by the Division of Pediatric Hematology and Oncology, Department of Pediatrics, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital, Bangkok, Thailand. The authors were grateful to all the staff of Hemophilia Treatment Center, Division of Pediatric Hematology and Oncology, Department of Pediatrics, and the Musculoskeletal Imaging Unit, Division of Diagnostic Radiology, Department of Radiology, Faculty of Medicine, Chulalongkorn University and King Chulalongkorn Memorial Hospital, who are part of the comprehensive haemophilia care team and the HEAD-US score evaluation, respectively. This study was supported by the Ratchadapisek Research Funds (grant no. GA68/096), the Faculty of Medicine, Chulalongkorn University. This study had received the ethical approval from the Institutional Review Board of the Faculty of Medicine, Chulalongkorn University (IRB no. 0736/67). The research procedure adhered strictly to the principles of the Declaration of Helsinki. All participants and/or their legal guardians provided their informed written consent prior to enrolment. The authors declare no conflicts of interest. A.P. and D.S. have full access to all data and take responsibility for the integrity and accuracy of data. The data that support the findings of this study are available from the corresponding author upon reasonable request. Supplementary Figure S1: Study design. Supplementary Table S1: Characteristics of 18 patients with severe haemophilia A participating in the study. Supplementary Table S2: Assay techniques used for biomarker measurements in the study. 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