From the Guidelines
Spirometry results should be interpreted by examining key measurements like FEV1, FVC, and the FEV1/FVC ratio, with a post-bronchodilator fixed ratio of FEV1/FVC less than 0.70 indicating airflow limitation, as recommended by the 2017 Global Strategy for the Diagnosis, Management, and Prevention of Chronic Obstructive Lung Disease report 1. To interpret spirometry results, healthcare professionals should consider the following key points:
- Normal spirometry is defined by an FEV1/FVC ratio above 0.7 (or 70%) and FEV1 and FVC values at or above 80% of predicted values based on age, height, sex, and ethnicity.
- An obstructive pattern is indicated by a reduced FEV1/FVC ratio below 0.7, with severity determined by the FEV1 percentage (mild: 60-79%, moderate: 40-59%, severe: below 40%).
- A restrictive pattern shows normal or increased FEV1/FVC ratio but reduced FVC (below 80% predicted).
- Bronchodilator response testing is important for assessing reversibility of airflow limitation, with a significant response suggesting conditions like asthma. The clinical context is crucial in interpreting spirometry results, as they should be evaluated alongside symptoms, medical history, and other diagnostic tests for accurate diagnosis and treatment planning, as noted in the 2011 American College of Physicians guideline update 1. The use of spirometry results to promote smoking cessation has been studied, but the evidence suggests that obtaining and providing individuals with spirometry results does not independently improve smoking cessation or the likelihood of continued abstinence 1. In terms of monitoring disease status or modifying therapy in symptomatic patients, the evidence does not support the use of routine periodic spirometry after initiation of therapy, as improvements in clinical symptoms do not necessarily correlate with spirometric responses to therapy or reduction of long-term decline in FEV1 1.
From the Research
Interpreting Spirometry Results
To interpret spirometry results, several steps and considerations must be taken into account, as outlined in various studies 2, 3, 4. The process involves:
- Determining the validity of the test, which is crucial for accurate interpretation 2.
- Identifying whether an obstructive or restrictive ventilatory pattern is present, based on measurements such as the forced expiratory volume in the first second (FEV1) and the vital capacity (VC) 3.
- Grading the severity of the ventilatory pattern if one is identified 2.
- Considering additional tests for some patients, such as static lung volumes, diffusing capacity of the lung for carbon monoxide, and bronchodilator challenge testing, which can provide further insight into lung function but require more advanced equipment and expertise 2.
Key Measurements in Spirometry
The key measurements in spirometry include:
- Forced expiratory volume in the first second (FEV1) 3, 5.
- Vital capacity (VC) 3, 5.
- The FEV1/VC ratio, which is critical for diagnosing and assessing the severity of airway obstruction in conditions like chronic obstructive pulmonary disease (COPD) 3, 5.
Accuracy and Reliability of Office Spirometry
Office spirometry (OS) has been found to correlate well with laboratory spirometry (LS) in patients with symptomatic obstructive lung disease, including asthma and COPD 5. This suggests that OS can be a reliable and accurate tool for diagnosing and managing these conditions when proper equipment and techniques are used.
Challenges and Advances
Despite its utility, spirometry remains underutilized, and its parameters are sometimes misinterpreted 6. Advances in spirometry testing, including new metrics and reference equations, as well as technological improvements in equipment, aim to increase access and improve the interpretation of spirometry results 6. However, challenges such as the need for more diverse reference populations and limitations in predicted values for certain measurements remain 6.