Identifying thresholds for meaningful improvements in NTDT-PRO scores to support conclusions about treatment benefit in clinical studies of patients with non-transfusion-dependent beta-thalassaemia: analysis of pooled data from a phase 2, double-blind, placebo-controlled, randomised trial

Abstract

Objectives To estimate thresholds for defining meaningful within-patient improvement from baseline to weeks 13–24 and interpreting meaningfulness of between-group difference for the non-transfusion-dependent beta-thalassaemia patient-reported outcome (NTDT-PRO) tiredness/weakness (T/W) and shortness of breath (SoB) scores. A secondary objective was to determine the symptom severity threshold for the NTDT-PRO T/W domain to identify patients with symptomatic T/W.Design Pooled blinded data from the phase 2, double-blind, placebo-controlled, randomised BEYOND trial in NTDT (NCT03342404) were used. Anchor-based analyses supplemented with distribution-based analyses and empirical cumulative distribution function (eCDF) curves were applied. Distribution-based analyses and receiver operating characteristic curves were used to estimate between-group difference and symptomatic thresholds, respectively.Setting Greece, Italy, Lebanon, Thailand, the UK and the USA.Participants Adults (N=145; mean age 39.9 years) with NTDT who were transfusion-free ≥8 weeks before randomisation.Measures Score changes from baseline to weeks 13–24 in PROs used as anchors (correlation coefficient ≥0.3): NTDT-PRO T/W and SoB scores, Patient Global Impression of Severity, Functional Assessment of Chronic Illness Therapy–Fatigue (Fatigue Subscale, item HI12 and item An2) and Short Form Health Survey version 2.Results The eCDF curves support the use of estimates from the improvement by one level group for all anchors to determine the threshold(s) for meaningful within-patient improvement. Mean (median) changes from these groups and estimates from distribution-based analyses suggest that a ≥1-point reduction in the NTDT-PRO T/W or SoB domains represents a clinically meaningful improvement. Meaningful between-group difference threshold ranges were 0.53–1.10 for the T/W domain and 0.65–1.15 for the SoB domain. The optimal symptomatic threshold for the T/W domain (by maximum Youden’s index) was ≥3 points.Conclusions The thresholds proposed may support the use of NTDT-PRO in assessing and interpreting treatment effects in clinical studies and identifying patients with NTDT in need of symptom relief.