Symptoms and markers of symptom severity in asthma--content validity of the asthma symptom diary

The American Thoracic Society/European Respiratory Society (ATS/ERS) Task Force acknowledged the multi-faceted nature of asthma in its recent definition of asthma control as a summary term capturing symptoms, reliever use, frequency/severity of exacerbations, lung function, and future risk and the Global Initiative for Asthma (GINA) defines the clinical manifestations (well established markers of asthma severity) of asthma to include symptoms, sleep disturbances, limitations of daily activity, impairment of lung function, and use of rescue medications. The objectives of this qualitative work were to identify symptoms and markers of symptom severity relevant to patients with moderate to severe asthma and to evaluate the content validity of the asthma symptom diary (ASD).

A qualitative interview study was conducted using a purposive sample of symptomatic adult and adolescent (≥12 years) subjects with asthma. Concept elicitation (CE) interviews (n = 50) were conducted to identify core asthma symptoms and symptom-related clinical markers, followed by cognitive interviews (n = 24) to ensure patient comprehension of the items, instructions and response options. CE interviews were coded using ATLAS.ti for content analysis.

The study sample had a diverse range of symptom severity, level of symptom control, sociodemographic and socioeconomic status. The most frequently reported symptoms in adults were chest tightness (n = 33/34; 97.1%), wheezing (n = 31; 91.2%), coughing (n = 30; 88.2%), and shortness of breath (n = 25; 73.5%); in adolescents they were wheezing (n = 14/16; 87.5%), coughing (n = 13; 81.3%), and chest tightness (n = 11; 68.8%). Adults identified chest tightness followed by shortness of breath as their most severe symptoms; while adolescents reported coughing and chest tightness as their most severe symptoms. Sleep awakenings and limitations in day-to-day activities were frequent symptom-related clinical markers. Day-to-day variability and differences between daytime and nighttime symptom experiences reported by subjects resulted in the need for the ASD to be administered twice daily. Cognitive interviews indicated that subjects found the revised ASD items clear and easy to understand.

This study supports the content validity of the revised ASD, showing it to be consistent with patient experiences and ready for further psychometric testing.