Asthma

Diagnosis of asthma

The symptoms of asthma are non-specific and shared with other diseases, which can make diagnosis challenging.¹ With no consistent gold-standard diagnostic criteria, the diagnosis of asthma is a clinical one.² Whilst tests may help to influence the probability of asthma, they alone are not sufficient to prove a diagnosis.²

A diagnosis of asthma should be considered based on a particular pattern of respiratory symptoms, clinical history and examination and lung function tests to document variability of airflow limitation.^3,4

Asthma should be considered in patients with the following pattern of respiratory symptoms and history:^3,4

A diagnosis of asthma is more likely in patients presenting with respiratory symptoms of wheeze, dyspnea, cough and/or chest tightness, and:³

• Generally, more than one type of respiratory symptom (especially in adults)³
• Symptoms which are often worse at night or early in the morning³
• Symptoms which vary over time and intensity³
• Symptoms which are triggered by exercise, allergens, changes in weather, laughter or irritants³
• Symptoms which often appear or worsen with viral infections³
• A personal or family history of atopic disorders⁴

Examine patients with suspected asthma^3,4

Physical examination can help to identify expiratory polyphonic wheeze and signs of other causes of respiratory symptoms, but it is not conclusive, as patients with normal examination results may still have asthma⁴

Consider tests to document airflow obstruction or variability in airflow obstruction^2-4

Spirometry to check for airflow obstruction (for adults, young people and children aged ≥5):⁴

• Airflow obstruction is defined by a post-bronchodilator FEV₁ /FVC <70%⁴

Bronchodilator reversibility to demonstrate variability in airway obstruction (offer to adults and consider in children with obstructive spirometry):^2,4

• In adults (ages 17 years and above), an improvement in FEV₁ ≥12% and increase in volume of ≥200 ml should be considered a positive test^2-4
• In children (ages 5–16 years), an improvement in FEV₁ ≥12% should be considered a positive test^2-4

Peak expiratory flow variability to provide an estimate of variability of airflow over a period of time from multiple measurements made over 2 to 4 weeks^1,2,4

• A value of more than 20% variability is regarded as a positive test⁴

Direct bronchial challenge test with histamine or methacholine to measure airway hyperreactivity (consider in adults with no evidence of airflow obstruction on initial assessment in whom other objective tests are inconclusive but asthma remains a possibility)^2-4

• Regard a PC20 value ≤8 mg/ml as a positive test⁴

Other tests

A fractional exhaled nitric oxide (FeNO) test can be used to find evidence of eosinophilic inflammation, and a positive test provides supportive, but not conclusive, evidence of asthma²

A negative FeNO test does not exclude asthma²

A FeNO test should be offered to adults (and considered in children where there is diagnostic uncertainty after initial assessment with normal spirometry or obstructive spirometry with a negative bronchodilator reversibility):⁴

• In adults, a FeNO level of ≥40 parts per billion is considered a positive test⁴
• In children, a FeNO level of ≥35 parts per billion is considered a positive test⁴

It should be noted that smoking may impact FeNO test results, as it can decrease FeNO levels²