Background: Asthma can be classified based on the status of type 2 (T2) inflammation. However, there is lack of information on its long-term stability.

Objective: To assess the stability of T2 inflammation and clinical features that are associated with T2-low or T2-high inflammation in patients with adult-onset asthma.

Methods: Seinäjoki Adult Asthma Study is a 12-year follow-up study including 256 patients diagnosed with new-onset adult asthma. At diagnosis, patients were classified as T2-high or T2-low based on blood eosinophil counts (cut off 0.30×109·L?1) and skin prick test results. At the follow-up, patients were grouped based on blood eosinophil counts, FeNO (cut off 25 ppb) and specific IgE antibody panel.

Results: At diagnosis, before initiation of inhaled corticosteroid therapy, 66.5% had T2-high and 33.5% T2-low asthma. T2-low patients were older, had higher BMI, more comorbidities, more non-respiratory medication, and higher interleukin-6 levels. T2-high patients had higher FEV1 reversibility. Of the patients presenting with T2-low characteristics at diagnosis, 42 (76%) remained T2-low and 13 (24%) transitioned to T2-high. Those who transitioned to T2-high had higher BMI. Of the patients that were T2-high at diagnosis, 74 (68%) remained T2-high and 35 (32%) transitioned to T2-low during therapy for 12 years. Those who transitioned to T2-low were older, had more comorbidities, and more non-respiratory medication.

Conclusions: Seventy one percent of the patients did not change their T2 inflammatory profile during the 12-year follow-up. T2-high and T2-low groups did not differ in terms of asthma outcomes but differed in demographic characteristics and comorbidities.