From the Guidelines
Interpreting spirometry requires analyzing key measurements, including FEV1 and FVC values, and comparing them to predicted normal values based on age, height, gender, and ethnicity, as recommended by the most recent guidelines 1. To interpret spirometry, first examine the FEV1 (forced expiratory volume in one second) and FVC (forced vital capacity) values. The FEV1/FVC ratio is crucial—a value below 70% suggests airflow obstruction typical of conditions like asthma or COPD. For obstructive patterns, look for reduced FEV1 with normal or reduced FVC, resulting in a decreased ratio. In restrictive patterns, both FEV1 and FVC are reduced proportionally, maintaining a normal or increased ratio. Some key points to consider when interpreting spirometry include:
- Severity classification depends on the percent of predicted FEV1: mild (>70%), moderate (60-69%), moderately severe (50-59%), severe (35-49%), and very severe (<35%) 1.
- Bronchodilator response testing is important—improvement in FEV1 by ≥12% and ≥200mL after bronchodilator administration indicates reversible airway obstruction, suggesting asthma rather than fixed obstruction 1.
- Flow-volume loops provide additional visual information: a scooped-out expiratory curve suggests obstruction, while a proportionally reduced but normally shaped curve indicates restriction 1.
- Always ensure proper test technique with at least three acceptable efforts and reproducible results to make accurate interpretations 1.
- PFT interpretations should be clear, concise, and informative, taking into consideration the pre-test probability of disease, the quality of the test results, and the clinical question to be answered 1.
From the Research
Interpreting Spirometry Results
To interpret spirometry results, it is essential to understand the different parameters measured and their significance in diagnosing and managing respiratory diseases. Spirometry is a common pulmonary function test that measures how well a person inhales and exhales air.
- Forced Expiratory Volume (FEV1): This measures the amount of air a person can exhale in one second. A lower FEV1 indicates obstructive lung disease, such as chronic obstructive pulmonary disease (COPD) or asthma 2, 3.
- Forced Vital Capacity (FVC): This measures the total amount of air a person can exhale after a maximum inhalation. A lower FVC indicates restrictive lung disease 4, 5.
- FEV1/FVC Ratio: This ratio helps diagnose obstructive and restrictive lung diseases. A lower ratio indicates obstructive lung disease, while a normal or higher ratio indicates restrictive lung disease 3, 6.
Clinical Applications of Spirometry
Spirometry is crucial in diagnosing and managing various respiratory diseases, including:
- Asthma: Spirometry helps diagnose asthma and monitor the effectiveness of treatment. A significant increase in FEV1 after bronchodilator administration indicates reversible airway obstruction, characteristic of asthma 2, 5.
- COPD: Spirometry is used to diagnose and stage COPD. The FEV1/FVC ratio is essential in diagnosing COPD, and the FEV1 value helps determine the disease severity 3, 4, 6.
- Asthma-COPD Overlap: Spirometry helps identify patients with overlapping features of asthma and COPD. These patients may require combination therapy, such as inhaled corticosteroids and long-acting beta-agonists (LABAs) 2.
Treatment Implications
Spirometry results guide treatment decisions, including:
- Bronchodilator Therapy: Spirometry helps assess the response to bronchodilators, such as salmeterol, and guides treatment adjustments 3, 5.
- Inhaled Corticosteroids: Spirometry results help determine the need for inhaled corticosteroids, such as fluticasone, in patients with asthma or COPD 2, 4, 6.
- Combination Therapy: Spirometry results guide the use of combination therapies, such as salmeterol-fluticasone, in patients with asthma, COPD, or asthma-COPD overlap 2, 3, 4, 6.