OBJECTIVE: We performed a systematic review of the prevalence of mild-to-moderate asthma in adolescents and adults using sputum inflammatory cell analysis and their responses to ICS.

METHODS: We searched electronic databases (PubMed, Scopus, EMBASE, Cochrane) for studies in adolescents and adults with mild-to-moderate asthma. The primary outcome was the prevalence of asthma subtypes based on sputum inflammatory cell analysis, categorized into EA and NEA. The secondary outcome involved comparing asthma outcomes between different subtypes after ICS therapy. Certainty of evidence was reported for each pooled analysis.

RESULTS: Eighteen studies involving 3,533 adolescents and adults with mild-to-moderate asthma were reviewed. The pooled prevalence (95% confidence interval) of NEA was estimated at 40.39% (27.54, 53.93) in patients with ICS naive with very low certainty of evidence. On reevaluating sputum cytology, the disease of approximately 20% to 30% of patients initially diagnosed as NEA transitioned to the EA subtype. EA patients showed significant improvements in asthma symptoms after ICS therapy: forced expiratory volume in 1 second (standardized mean difference, 0.79; 95% confidence interval, 0.30, 1.27), and airway hyperresponsiveness (standardized mean difference, 1.34; 95% confidence interval, 0.29, 2.40). NEA patients exhibited limited response.