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Objective: Adult-onset asthma is a recognized but heterogeneous phenotype and has been described to associate with poor asthma control. Knowledge about associations between clinical characteristics including comorbidities and control of adult-onset asthma is limited, especially in older populations. We aimed to study how clinical biomarkers and comorbidities are associated with uncontrolled asthma among middle-aged and older individuals with adult-onset asthma.

Methods: Clinical examinations including structured interview, asthma control test (ACT), spirometry, skin prick test (SPT), blood sampling, and measurement of exhaled fractional nitric oxide (FeNO) was performed in a population-based adult-onset asthma cohort in 2019–2020 (n = 227, 66.5% female). Analyses were performed among all included, and separately in middle-aged (37–64 years, n = 120) and older (≥65 years, n = 107) participants.

Results: In bivariate analysis, uncontrolled asthma (ACT ≤ 19) was significantly associated with a blood neutrophil count ≥5/µl, BMI ≥30, and several comorbidities. In multivariable regression analysis, uncontrolled asthma was associated with neutrophils ≥5/µl (OR 2.35; 95% CI 1.11–4.99). In age-stratified analysis, BMI ≥30 (OR 3.04; 1.24–7.50), eosinophils ≥0.3/µl (OR 3.17; 1.20–8.37), neutrophils ≥5/µl (OR 4.39; 1.53–12.62) and allergic rhinitis (OR 5.10; 1.59–16.30) were associated with uncontrolled asthma among the middle-aged. Among the older adults, uncontrolled asthma was only associated with comorbidities: chronic rhinitis (OR 4.08; 1.62–10.31), ischemic heart disease (OR 3.59; 1.17–10.98), malignancy (OR 3.10; 1.10–8.73), and depression/anxiety (OR 16.31; 1.82–146.05).

Conclusions: In adult-onset asthma, comorbidities were strongly associated with uncontrolled asthma among older adults, while clinical biomarkers including eosinophils and neutrophils in blood were associated with uncontrolled asthma among middle-aged.