The overall objective is to establish a clinical register for patients with severe asthma. Since the number of patients with severe asthma at a single center is usually low, it will be important to collect data in a multi-center system to optimize the diagnostic evaluation and treatment of patients with severe asthma. So far, there is little reliable information about the frequency, phenotype and therapy of patients with severe asthma. The construction of a clinical register should close this gap. The primary objective is to show changes in symptoms control during follow up period and at study end by using the Asthma Control Test (ACT). Secondary endpoints are to collect data to better understand asthma's natural history in patients with severe asthma. The examination will be based on the assessment of the parameters specified under "outcomes".

Patients presenting to participating study center (pulmonologists in private practice or in pulmonary departments in hospital within Switzerland) with severe asthma will be asked to take part in this study when corresponding to the eligibility criteria. All patients with severe asthma will be included in the register only after detailed information and written consent. After four months (for specific therapies) and after 12 months, patients should be re-evaluated for up to 15 years. These follow-up data will also be recorded in the register. During the follow-up visits, the same parameters will be collected as during the initial Baselineexamination (some parameters will be omitted, for example, therapy received or requested for the defined period of the last 12 months, etc.). Severe asthma patients receiving a new specific therapy, e.g. obtained with antibodies, but who cannot be included in the register with the complete parameter profile due to time or capacity reasons of the centers, should be recorded at least with defined basic data and a reduced number of parameters in the register. These parameters include according to the specific asthma approved specific therapies, socio-demographic data, lung function values, laboratory values, parameters of asthma control, smoking status and add-on- therapy. This should make it possible to record a subgroup of severe asthmatics that are suitable for antibody therapy and at the same time offer the attending physician the opportunity to adequately document these complex and expensive therapies by recording the defined parameters. In these patients, an evaluation of the therapy response should be carried out after four months and documented in the register. Thereafter, there is an annual follow-up. At any time, these patients can be transferred to the full version of the register by entering the missing parameters. Patients for whom only the basic data is available (basic version) as well as patients with complete parameter profile in the register are kept in the same database and can be evaluated together. In general, no register-specific examinations will be carried out, but only parameters anyway recorded routinely.

Since this is a cohort study, no sample size calculation can be calculated. Evaluations are carried out continuously. The collective of the data should be described by descriptive statistics concerning the basic data as well as the data of the function diagnostics. Subentities of severe asthma should be identified by a cluster analysis.