Asthma in adults

There are no widely accepted consistent gold-standard diagnostic criteria for asthma. Central to all definitions is the presence of symptoms (more than one of wheeze, breathlessness, chest tightness, cough) and of variable airflow obstruction. For information specific to diagnosing exacerbations, see Acute asthma exacerbation in adults.

British Thoracic Society/Scottish Intercollegiate Guidelines Network (BTS/SIGN)[55]British Thoracic Society; Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma: a national clinical guideline. Jul 2019 [internet publication]. https://www.sign.ac.uk/sign-158-british-guideline-on-the-management-of-asthma

BTS/SIGN recommend a clinical diagnosis based on clinical assessment supported by objective tests that demonstrate variable airflow obstruction or the presence of airway inflammation. Use this information to establish whether the patient's likelihood of having asthma is of high, intermediate, or low probability.[55]British Thoracic Society; Scottish Intercollegiate Guidelines Network. British guideline on the management of asthma: a national clinical guideline. Jul 2019 [internet publication]. https://www.sign.ac.uk/sign-158-british-guideline-on-the-management-of-asthma

• High probability of asthma (all of the following typical features):

  • Recurrent episodes of symptoms ('attacks')

  • Wheeze confirmed by a healthcare professional

  • A positive history of atopy

  • A historical record of variable airflow obstruction

  • No features to suggest an alternative diagnosis.

• Intermediate probability of asthma:

  • Some but not all of the typical features (listed above) or

  • A poor response to an initial trial of treatment.

• Low probability of asthma

  • None of the typical features of asthma (listed above) or

  • Presents with features more suggestive of an alternative diagnosis.

Global Initiative for Asthma (GINA)[1]Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention. 2024 [internet publication]. https://ginasthma.org/reports

According to the international guidelines from GINA, asthma is defined by a history of respiratory symptoms, such as wheeze, shortness of breath, chest tightness, and cough, that vary over time and in intensity, together with confirmed variable expiratory airflow limitation.[1]Global Initiative for Asthma (GINA). Global strategy for asthma management and prevention. 2024 [internet publication]. https://ginasthma.org/reports

Variable respiratory symptoms

• Symptoms vary over time and in intensity

• Symptoms are often worse at night, or on waking

• Symptoms may be triggered by exercise, laughter, allergens, or cold air

• Symptoms may appear or worsen with viral infections

Confirmed variable expiratory airflow limitation

• Consists of documented excessive variability in lung function and documented expiratory airflow limitation.

• Peak expiratory flow (PEF) measurement can be used as an alternative to spirometry where spirometry services are not available. Although the PEF is less reliable than spirometry, its use is preferred where diagnosis would otherwise rely on symptoms only. Use the highest of three readings and the same meter at each measurement over time.

• At a time when forced expiratory volume at 1 second (FEV₁) is reduced, a reduced FEV₁/forced vital capacity (FVC) ratio from spirometry indicates airflow limitation. Adults without airflow limitation normally have an FEV₁/FVC ratio of >0.75 to 0.80.

• One or more of the following tests confirms excessive variability in lung function. The greater the variations, or the more occasions that excess variation is seen, then the more likely is the diagnosis of asthma. Tests can be repeated during symptoms or early in the morning if initially negative:

  • A positive bronchodilator responsiveness (reversibility) test; more likely to be positive if bronchodilator medication is withheld before test: short-acting beta agonist (SABA) ≥4 hours, twice-daily long-acting beta agonist (LABA) 24 hours, once-daily LABA 36 hours. In adults, an increase in FEV₁ of >12% and >200 mL from baseline (or PEF of ≥20%), 10 to 15 minutes after 200-400 micrograms of salbutamol (albuterol) or equivalent, is a positive test; there is greater diagnostic confidence if the increase is >15% and >400 mL.

  • Excessive variability in twice-daily PEF over 2 weeks (subtract each day’s highest from each day’s lowest value and divide by the mean). In adults, an average daily diurnal variability in PEF of >10% is considered excessive.

  • A significant increase in lung function after 4 weeks of anti-inflammatory treatment. In adults, an increase in FEV₁ by >12% and >200 mL (or PEF by ≥20%) from baseline after 4 weeks of treatment, outside respiratory infections, indicates excessive variability.

  • A positive exercise challenge test. In adults, a fall in FEV₁ of >10% and >200 mL from baseline is a positive test.

  • A positive bronchial challenge test. A fall in FEV₁ from baseline of ≥20% with standard doses of methacholine, or ≥15% with standardised hyperventilation, hypertonic saline, or mannitol challenge.

  • Excessive variation in lung function between visits: good specificity but poor sensitivity. In adults, a variation in FEV₁ of >12% and >200 mL between visits (or PEF of ≥20%), outside of respiratory infections, indicates excessive variability.