Justifying score interpretation thresholds for the Asthma Control Questionnaire (ACQ-5) in a contemporary asthma patient population.

Asthma is a chronic inflammatory lung disease, characterized by recurrent episodes of breathlessness, wheezing, chest tightness, and cough, which make it difficult to breathe [, ]. It is one of the most prevalent chronic, non-communicable diseases, affecting an estimated 334 million people worldwide []. Asthma symptoms can vary over time and intensity, with variable expiratory airflow limitation [, ]. Symptoms may resolve spontaneously or in response to treatment [, ]. The long-term goals of asthma management are to achieve good symptom control (e.g., few or no asthma symptoms, unimpaired physical activity, no sleep disturbances) and minimize asthma-associated risks (e.g., future exacerbations, fixed airflow limitation, maintenance systemic corticosteroids, asthma-related deaths) []. Treatment options include inhaled corticosteroids-containing medication (ICS) in isolation, when taking a short-acting beta antagonist, or in combination with a long-acting beta-agonist (LABA). Reliever inhalers for symptom relief and add-on controller medications are also available for patients with severe disease []. Patients with severe asthma that is inadequately controlled using standard inhaled or oral medications may also be prescribed biologic therapies to help improve disease control []. Despite these available therapies, a large proportion of patients experience inadequately controlled asthma [–]. The 5-item Asthma Control Questionnaire (ACQ-5) is a patient-reported outcome (PRO) measure designed to assess the adequacy of asthma symptom control and changes in symptom control as a result of treatment []. The ACQ-5 has frequently been used to support asthma clinical trial endpoints to demonstrate changes in asthma symptom control following treatment []. To assess such changes, an understanding of the amount of change in ACQ-5 scores that is meaningful to patients is needed. A meaningful improvement threshold of ≥ 0.5 has been proposed in the literature [] and has been used to support endpoints in asthma trials [–]. However, recent developments within the score interpretation literature have led to contemporary recommendations to derive both within-individual and between-group thresholds [], and currently there is ambiguity as to whether the extant 0.5 threshold is applicable to between-group difference and meaningful within-patient change (MWPC) [, , ].