Protocol, rationale and design of the PHOLLOW cross-sectional and retrospective chart review study to assess the prevalence and characterize the patient profile, clinical features and disease burden of type-2 low severe asthma in routine care settings in Greece

Type 2 (T2)-low severe asthma (SA) presents a distinct subpopulation for which, in lack of a consistent classification system, epidemiological and clinical outcome data remain unclear and therapeutic needs remain largely unmet. The aim of the PHOLLOW real-world study is to assess the prevalence and predictors of T2-low SA, and depict the patient profile, clinical features, treatment patterns and disease burden using clinical and patient-reported outcomes (PROs) in routine settings in Greece. This is a cross-sectional and retrospective chart review 2-part study that will enroll 600 adult outpatients with SA over a 1-year period by 20–30 asthma specialists. A new SA phenotype classification system and two different definitions proposed herein will be used to categorize patients into definite or possible T2-low (unlikely or least likely T2-high) SA, and definite/most likely or possible/likely T2-high SA, based on a composite measure of airway inflammation markers (blood eosinophil counts, fractional exhaled nitric oxide), allergic/atopic status and age-of-onset phenotype, taking into consideration the current receipt of biologic and/or maintenance oral corticosteroid treatment and response to it. Part A will collect top-level data for all participants to assess T2-low SA prevalence and predictors. T2-low SA patients will proceed to part B, where further data and PROs assessing asthma symptom control, quality of life, anxiety, depression, work productivity and activity impairment will be collected.