Introduction Many conditions may mimic severe asthma. Therefore, patients with asthma who receive high dose asthma therapy are recommended to undergo systematic evaluation in order to objectively confirm the diagnosis of asthma.

Aims and objectives To evaluate to which extent patients treated by respiratory specialists for severe asthma had the diagnosis of asthma verified by the demonstration of variable airflow obstruction.

Methods A retrospective cross-sectional study was performed in 2013. Patient record forms of all patients (18–65 years) newly referred to one of five respiratory outpatient clinics in Denmark in the period of 2009–2010 with a diagnose of asthma (ICD-10: DJ45-DJ459) were screened after a two-year observation period for having severe asthma. Patients were included in the study, if they had a doctors diagnosis of asthma and received inhaled corticosteroids equivalent to ≥1600 μg budesonide and a second controller (long acting beta-2-agonist, theophylline or leukotriene-antagonist) for a minimum of twelve months or were treated with oral prednisolone (minimum six months). Diagnostic tests for asthma were registered: Day-to-day PEF monitoring, reversibility test (short-acting beta-2-agonist or prednisolone) and bronchial challenge test (methacholine, mannitol, exercise test, eucapnic voluntary hyperpnoea test).

Results A total of 1417 newly referred subjects were screened, of whom 98 patients fulfilled the above criteria of having severe asthma. Overall, 84% were assessed with at least one diagnostic test: Reversibility test 63%, PEF monitoring 57% and bronchial challenge test 21%.

In total, 50% of the study population had at least one positive diagnostic test; 37% had a positive reversibility test, 17% had significant peak flow variation and 12% had a positive bronchial challenge test. Among those having negative reversibility test or negative peak flow measurements with FEV1≥70%, only 30% had a bronchial challenge test performed.

Conclusion Among patients managed for severe asthma in five specialist hospital clinics in Denmark, only half had the asthma diagnosis confirmed objectively. This indicates a substantial room for improvement in order to ensure that patients receiving high dose asthma therapy truly have asthma.