The latest European Respiratory Society Guidelines for the Diagnosis of Asthma in Adults were published in 2022. This article discusses their importance, their definition of asthma, and the most important recommendations on the test to use in diagnosing this condition.
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The European Respiratory Society (ERS) is one of the leading associations focused on promoting research and education in respiratory medicine in Europe and beyond. It was founded in 1990 and has become one of the largest and most influential respiratory organisations in the world, with 32,000 members from more than 160 countries. 
The ERS makes an important difference to asthma management in several ways.
Firstly, it enables idea exchange and collaboration on research related to respiratory diseases, also by funding research projects and awarding them. This helps develop new treatments and management strategies.
Secondly, the ERS organises conferences, workshops and training focused on respiratory medicine. This enables medical professionals to stay up-to-date on the latest findings and good practice cases.
Thirdly, the ERS produces guidelines and recommendations for the diagnosis, treatment, and management of respiratory diseases, including asthma.
ERS guidelines are evidence-based, widely recognised and regularly updated. They are developed by a panel of respiratory medicine experts and based on the latest evidence from research studies. They are regularly updated according to the developments in the field. This means that healthcare professionals can be confident that they are providing their patients with the most up-to-date and effective treatments and management. All this contributes to better patient outcomes.
Asthma affects 5-10% of the population (339 million patients worldwide), but remains both under-and overdiagnosed.
The most important reason for the high false positive diagnosis rate (30%) is insufficient use of spirometry; rather, the diagnosis is often based on symptoms only. In secondary care, the most frequent problem is relying on the asthma diagnosis once it is made rather than thoroughly investigating the nature of the condition and monitoring it over time to make sure the diagnosis is correct. This leads to unnecessary or inappropriate medication, with negative effects on the patient. 
The asthma diagnosis is often made after many different tests, which, if positive, could also indicate many other conditions. Therefore, the diagnostic process is time-consuming and psychologically difficult for the patient.
The latest European Respiratory Society Guidelines for the Diagnosis of Asthma in Adults started being compiled in 2019 and were published in 2022. (It is important to note that they focus on diagnosing asthma rather than phenotyping.) They bring recommendations as to the paths of diagnosing asthma in adults with current symptoms in the form of an algorithm applicable to primary and secondary care. The panel consisted of GPs, specialists as well as patient representatives.
The ERS task force for creating the guidelines admits that this was one of the hardest parts of their work as everybody claims that they know what asthma is, but use different definitions.  The operating definition of the ERS task force was set as follows:
Both for primary and secondary care, asthma is defined as a combination of typical symptoms (breathlessness, cough, wheezing, chest tightness) and objective demonstration of excessive airway calibre fluctuation with at least one of the following results:
1. Peak flow variability ≥20% or spontaneous variation in FEV1 ≥12% and 200 ml
2. Reversibility after bronchodilator inhalation with improvement in FEV1 of ≥12% and 200 ml
3. Airway hyperresponsiveness: PC20-M (or H) <8 mg/ml (or 16 mg/ml in ICS treated patients), PD mannitol < 625 mg or FEV1 fall ≥10% after exercise
4. Improvement in FEV1 ≥12% and 200 ml after a two-week course of OCS or a 4-6 week course of ICS
FEV1: forced expiratory volume in 1 second
ICS: inhaled corticosteroid
OCS: oral corticosteroid PC20-H: provocation concentration causing 20% fall in FEV1 with histamine
PC20-M: provocation concentration causing 20% fall in FEV1 with methacholine
PD: provocation dose
The guidelines were created on the basis of the PICO (Patient/Problem, Intervention, Comparison and Outcome) framework, which is often used in evidence-based medicine to formulate clinical questions and facilitate literature review. PICO questions served to assess the tests for asthma at the primary and secondary levels. The research literature underwent a GRADE analysis. On this basis, recommendations were formed regarding each PICO question and a diagnostic algorithm was constructed, consisting of a series of diagnostic steps in the specific order presented below. 
Spirometry is underused in diagnosing asthma. Despite the low quality of evidence, it is strongly recommended as the initial step in detecting airway obstruction in adults. An FEV1/FVC <LLN or <75% should be regarded as supportive of an asthma diagnosis and warrant further testing. Nevertheless, a normal spirometry result does not exclude asthma.  
In case of doubt, initial spirometry should be combined with bronchodilator reversibility test. An improvement of FEV1 ≥12% and 200 ml should be considered as indicative of asthma.
Used if the diagnosis cannot be made by means of spirometry combined with bronchodilator reversibility. A cut-off of 50 ppb is supportive of an asthma diagnosis. However, values under 40 ppb do not exclude asthma and high FeNO levels are not necessarily a sign of it either. Conditions like allergic rhinitis or eosinophilic bronchitis may be associated with raised FeNO.
This method is used to show bronchial hyperresponsiveness, which is an important pathophysiological feature of asthma. There are two types of these tests: direct (with methacholine or histamine) and indirect (with exercise or mannitol).
In the case of values other than PC20-M (-H) < 8mg/ml or PD20-M < 200 μg, other diagnoses may be considered. They can include dysfunctional breathing, vocal cord dysfunction, gastroesophageal reflux disease (GERD), tracheobronchomalacia and chronic rhinosinusitis.
As the primary test in diagnosing asthma, PEF variability should only be used if no other lung function tests are available, e.g. spirometry or bronchial challenge testing.
While eosinophilic inflammation may contribute to the worsening of asthma, it can not be used in diagnosing it due to low quality of evidence.
This method is useful for phenotyping asthma rather than diagnosing it.
As all above tests can also indicate a number of other conditions, the patient’s history should always be considered. Additional comorbidities (e.g. smoking, obesity) may not only affect the individual management of asthma, but also the diagnosis itself.
To conclude, the current European Respiratory Society Guidelines for the Diagnosis of Asthma in Adults represent well-researched and highly recognised international recommendations on asthma diagnostics.