From the Guidelines
The gold standard for diagnosing asthma is spirometry with bronchodilator reversibility testing, as recommended by the most recent and highest quality study 1. This test measures lung function by having the patient forcefully exhale into a device that measures airflow. A diagnosis of asthma is supported when spirometry shows airflow obstruction (FEV1/FVC ratio less than 0.7 or below the lower limit of normal) that improves significantly after administration of a bronchodilator medication. Significant reversibility is defined as an increase in FEV1 of at least 12% and 200 mL after inhaling a short-acting beta-agonist like albuterol (salbutamol) 1. If spirometry results are normal but asthma is still suspected, additional tests may be needed, such as bronchial challenge testing with methacholine, exercise, or eucapnic voluntary hyperventilation 1. Peak expiratory flow (PEF) monitoring over 2-4 weeks can also help establish variability in airflow limitation. A thorough clinical history of episodic respiratory symptoms (wheezing, shortness of breath, chest tightness, and cough) that vary over time and in intensity, along with physical examination findings, should always complement these objective measurements. This comprehensive approach is necessary because asthma is characterized by variable airflow obstruction, and a single test may not capture this variability. The European Respiratory Society clinical practice guidelines for the diagnosis of asthma in children aged 5-16 years also recommend spirometry, bronchodilator reversibility testing, and exhaled nitric oxide fraction as first-line diagnostic tests 1.
Some key points to consider when diagnosing asthma include:
- Episodic symptoms of airflow obstruction or airway hyperresponsiveness are present 1
- Airflow obstruction is at least partially reversible, measured by spirometry 1
- History of symptoms such as cough, recurrent wheeze, recurrent difficulty in breathing, and recurrent chest tightness 1
- Symptoms occur or worsen in the presence of triggers such as exercise, viral infection, inhalant allergens, irritants, changes in weather, strong emotional expression, stress, menstrual cycles, and at night 1
- Physical examination findings such as wheezing, hyperexpansion of the thorax, use of accessory muscles, and appearance of hunched shoulders or chest deformity 1
- Spirometry can demonstrate obstruction and assess reversibility in patients 5 years of age and older 1
From the Research
Diagnosis of Asthma
The diagnosis of asthma is based on clinical symptoms, physical examination, and pulmonary function tests, and can be very challenging 2.
Pulmonary Function Tests
Pulmonary function tests, such as spirometry, are used to support the likelihood of an asthma diagnosis 3, 4.
- A significant postbronchodilator response on spirometry indicates airway hyperresponsiveness, but having a significant bronchodilator response by itself is not diagnostic of asthma 2.
- The American Thoracic Society (ATS) postbronchodilator response criteria of 12% improvement in forced expiratory volume in 1 s (FEV1) from the baseline spirometry is commonly used, but relying on spirometric criteria alone is inadequate in asthma diagnosis 2.
- A literature review suggests that a less stringent improvement in FEV1 in children might be applicable 3.
- The severity of the abnormality is determined by the FEV1 (percentage of predicted) 4.
Gold Standard for Diagnosing Asthma
There is no single gold standard for diagnosing asthma, and the diagnosis depends on expert physician correlation of patient history, physical examination, and pulmonary function test results 2, 5.
- Physiologic measures, such as baseline spirometry, post-bronchodilator FEV1, airway responsiveness, and ambulatory monitoring, contribute unique information when measuring asthma outcome in a clinical trial 5.
- Spirometric changes in bronchodilation tests, along with fractional exhaled nitric oxide (Feno), can predict the response to antiasthma therapy in patients with suspected asthma and normal FEV1 6.