Background: Lung function assessment is critical in asthma management. Although lung function data is routinely collected in clinical practice, it is often underrepresented in real-world data sources. Asthma severity (mild, moderate, or severe) and acute exacerbation status are often captured through diagnosis codes, yet their relationships to measured lung function are not well characterized.
Objectives: To assess lung function in patients with persistent asthma according to severity and acute exacerbation status as documented in International Classification of Diseases, 10th Edition (ICD-10) codes.
Methods: In this cross-sectional study, electronic health record data (2017-2025) from 3 integrated delivery networks in the OMNY Health real-world data platform was accessed. Patients were selected if they had a persistent asthma ICD-10 code classifiable as mild (J45.3x), moderate (J45.4x), or severe (J45.5x) with (J45.x1) or without (J45.x0) acute exacerbation. Additionally, patients had to have at least one documented forced expiratory volume in 1 second (FEV1) percent predicted (pp), forced vital capacity (FVC) pp, or FEV1/FVC pp associated with an asthma encounter. Demographic variables were summarized at first relevant asthma encounter, and descriptive statistics were generated for lung function variables by severity and acute exacerbation status.
Results: Approximately 1 million patients with asthma had an ICD-10 code to indicate severity and exacerbation status; 14,003 patients (across 31,463 encounters) had an associated lung function measurement. Distributions of gender (62% female), race (13% nonwhite), ethnicity (8% Hispanic or Latino), and age (mean: 43 years; standard deviation [SD]: 24 years) were similar across severity and exacerbation categories. Mean (SD) FEV1 pp for encounters associated with mild, moderate, and severe persistent asthma were 87.6 (17.6), 84.4 (18.7), and 81.6 (20.7) without exacerbation and 85.1 (18.3), 81.3 (19.1), and 74.4 (19.9) with exacerbation, respectively. Analogous values were 90.6 (17.4), 88.6 (17.4), and 88.3 (18.2) without exacerbation and 88.8 (18.2), 87.2 (17.9), and 83.3 (17.8) with exacerbation for FVC pp and 94.1 (15.7), 91.7 (15.4), and 85.7 (17.4) without exacerbation and 91.4 (16.4), 83.6 (17.6), and 82.6 (17.5) for FEV1/FVC pp.
Conclusions: This study provides insight into lung function during encounters with coded asthma severity and exacerbation status. Mean lung function metrics decreased monotonically with increasing severity regardless of exacerbation status. Encounters with coded exacerbations had consistently lower lung function metrics. Severity as derived from ICD-10 codes did not correspond well to accepted cutoff lung function values for mild, moderate, and severe disease.
