Background: Phenotype and severity of asthma influence treatment choice, asthma control, and quality of life. Therefore, it is essential to understand the prevalence of various subgroups.

Aims: To assess the prevalence of asthma, severe asthma, and severe eosinophilic asthma among Finnish adults.

Methods: All Finnish adults who had asthma diagnosis either in the secondary (ICD-10: J45) or primary care (ICD-10: J45 or ICPC-2: R96) during 2014?2019 were included in the study. Asthma was categorized as severe based on dispensed ICS and OCS doses, hospitalizations, and use of biological treatments. Eosinophilic asthma was assessed among those with severe asthma and at least one blood eosinophil count (bEos) available. Severe asthma was regarded as eosinophilic when bEos was ?0.3x10⁹/l at least once, non-eosinophilic when all bEos values were <0.3x10⁹/l (at least 3 counts available) and difficult-to-classify if 1-2 bEos values were available and were <0.3x10⁹/l.

Results: The study population included 278,172 adult patients with a primary or secondary care asthma diagnosis corresponding to a population prevalence of 6%. Altogether, 137,772 individuals (50% of the study population) had asthma diagnosis in secondary care and 12,679 (9%) of these patients had severe asthma. Data on bEos count was available for 4,178 patients with severe asthma. A total of 2,256 (54%) of these patients were classified as eosinophilic, 837 (20%) as non-eosinophilic, and 1,085 (26%) as difficult to classify.

Conclusions: The prevalence of asthma was estimated to be 6% in the adult Finnish population. Among the secondary care asthma patients, 9% had severe asthma and 54% of them had eosinophilic severe asthma. Funded by GSK (ID219294).