Finding the smallest detectable change (SDC) of the haemophilia activities list (HAL): preliminary results

Introduction: The Haemophilia Activities List (HAL) measures self-reported limitations in activities and participation in adult patients with haemophilia. The Smallest Detectable Change (SDC) is a measure for reliability; it is the smallest change in score that you can detect above the measurement error. This study aimed to determine the SDC of the HAL. Methods: Adult patients (≥18 years) with mild to severe haemophilia completed the HAL repeatedly between september 2017 – september 2018. The first HAL (T0) was completed during a visit at the Van Creveldkliniek, Utrecht, The Netherlands. The second HAL (T1) was sent by mail after three weeks and patients were asked to complete the questionnaire within one week. Patients were excluded if the had a recent bleed at T0 or T1. The HAL score ranges from 0-100, with 100 as optimum score. The SDC,agreement was calculated for sum and component scores. The SDC,agreement include the systematic difference. A total of 50 patients will be included in this study, according the COSMIN guidelines. Results: Thirty-seven patients with haemophilia A/B (24% mild/3% moderate/72% severe, median 52 years [range 20-79]) were included. The median (interquartile range [IQR:P25-P75]) HAL sum score at T0 was 73.5 (59.1-95.7). The median (IQR) HAL sum score at T1 was 77.8 (60.8-98.0). Median (IQR) time between measurement at T0 and T1 was 3.7 weeks (3.0-5.4). The SDC,agreement for the sum score was 9.3, for the basic lower extremity component 15.8, for the complex lower extremity component 13.6 and for the upper extremity component 9.6. Discussion/Conclusion: The SDC of the HAL sum score in Dutch patients with mild to severe haemophilia was 9.3, determined in this preliminary analysis with 37 patients. A change of the HAL >9.3 in one patient signifies a true change. To improve interpretation of HAL scores, the SDC should be combined with clinical patient evaluation (Minimally Important Change). This will establish the smallest change in score which patients perceive as important.