How is asthma diagnosed by spirometry (Spirometry)?

From the Guidelines

Asthma is diagnosed using spirometry by measuring airflow limitation and its reversibility, with a key diagnostic feature being bronchodilator reversibility, demonstrated by a 12% or greater improvement in FEV1 and an absolute increase of at least 200 mL after administration of a short-acting bronchodilator like albuterol. During a spirometry test, the patient forcefully exhales into a device that measures lung function parameters, particularly the forced expiratory volume in one second (FEV1) and forced vital capacity (FVC) 1. A diagnosis of asthma is supported when the FEV1/FVC ratio is less than 0.7 (or below the lower limit of normal), indicating airflow obstruction.

Key Diagnostic Features

• Bronchodilator reversibility, demonstrated by a 12% or greater improvement in FEV1 and an absolute increase of at least 200 mL after administration of a short-acting bronchodilator like albuterol (typically 400 mcg via metered-dose inhaler) 1
• FEV1/FVC ratio less than 0.7 (or below the lower limit of normal), indicating airflow obstruction
• Spirometry should be performed when patients are symptomatic for optimal diagnostic yield

Spirometry Test

• Measures lung function parameters, particularly FEV1 and FVC
• Patient forcefully exhales into a device
• Results are used to detect reversible airflow limitation caused by bronchial hyperresponsiveness and inflammation

Additional Testing

• If spirometry results are normal but asthma is still suspected, bronchial challenge testing may be performed using methacholine or exercise to provoke bronchoconstriction 1
• Other objective tests, such as FeNO testing, may be used to support a diagnosis of asthma 1

Clinical Practice

• Spirometry is an essential objective measure to establish the diagnosis of asthma, as medical history and physical examination are not reliable means of excluding other diagnoses or assessing lung status 1
• Spirometry should be performed by a trained operator, and results should be interpreted in the context of clinical symptoms and medical history 1

From the Research

Diagnosis of Asthma by Spirometry

• Spirometry is a crucial diagnostic tool for asthma, measuring the volume and speed of air inhaled and exhaled by the lungs 2, 3, 4, 5.
• A well-performed spirometry test can support the likelihood of an asthma diagnosis by assessing the change in forced expiratory volume in one second (FEV1) after administration of a bronchodilator, such as albuterol 2.
• The current standard for diagnosing asthma using spirometry is a 12% improvement in FEV1 after a bronchodilator, as recommended by the 2007 National Heart Lung and Blood Institute Asthma Expert Panel Report-3 (EPR-3) guidelines 2.

Interpretation of Spirometry Results

• A significant improvement in FEV1 after a bronchodilator suggests airway reversibility, which is a hallmark of asthma 3, 4.
• However, normal spirometry results do not rule out asthma, as patients with mild asthma may have normal lung function when asymptomatic 3.
• In patients with airway obstruction, a low diffusing capacity of the lung for carbon monoxide increases the probability of chronic obstructive pulmonary disease (COPD) and makes asthma less likely 3.

Spirometry in Clinical Practice

• Spirometry is an essential clinical measurement for the diagnosis, differentiation, and management of respiratory illnesses, including asthma, COPD, and restrictive lung disorders 5.
• The use of spirometry in primary care settings can improve patient understanding, confidence in self-management, and quality of life for those with lung disease 5.
• Spirometry may also be useful for monitoring the progress of patients with neuromuscular disease and incipient respiratory muscle weakness, as well as promoting respiratory health in the community setting 5.