How do you interpret spirometry results, including Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC)?

From the Guidelines

Interpreting spirometry results involves analyzing key measurements like FEV1 and FVC to assess lung function, with the FEV1/FVC ratio being particularly important, and values below 0.70 or 70% suggesting airflow obstruction. To interpret spirometry results, first examine the FEV1 (Forced Expiratory Volume in 1 second) and FVC (Forced Vital Capacity), and then calculate the FEV1/FVC ratio, which is crucial for diagnosing airflow obstruction, as seen in conditions like asthma or COPD 1. The severity of obstruction is determined by the FEV1 percentage of predicted value, with classifications including mild (>70%), moderate (60-69%), moderately severe (50-59%), severe (35-49%), and very severe (<35%) 1. A reduced FVC with a normal or increased FEV1/FVC ratio indicates restrictive lung disease. When interpreting results, consider the patient's age, height, sex, and ethnicity, as these factors influence predicted normal values 1. Also, note the bronchodilator response, as an improvement in FEV1 of ≥12% and ≥200mL after bronchodilator administration suggests reversible airway obstruction, typical of asthma. Some key points to consider when interpreting spirometry results include:

• The use of pre- and post-bronchodilator spirometry for the diagnosis of COPD, with the GOLD 2025 report recommending the use of pre-BD spirometry to rule out COPD and post-BD measurements to confirm the diagnosis 1.
• The importance of considering the patient's clinical presentation and risk factors, such as smoking or exposure to pollutants, when interpreting spirometry results 1.
• The potential for discordant results between pre- and post-BD spirometry, and the need for repeat testing in certain cases 1.
• The use of additional parameters, such as the FEV1/SVC ratio, to help diagnose airflow obstruction in certain cases 1. Always interpret spirometry in the context of clinical presentation, as results alone do not provide a definitive diagnosis but guide further evaluation and treatment decisions 1.

From the FDA Drug Label

The diagnosis of COPD was based upon a prior clinical diagnosis of COPD, a smoking history (greater than 10 pack-years), age (at least 40 years), spirometry results (prebronchodilator baseline FEV1 less than 70% of the predicted value, and at least 0. 75 liters, with the FEV1/VC being less than 88% for men and less than 89% for women) 2 Morning predose FEV1 was obtained at baseline and Endpoint (last available FEV1 result) in children aged 6 to 11 years. In subjects receiving fluticasone propionate and salmeterol inhalation powder 100 mcg/50 mcg, FEV1 increased from 1.70 L at baseline (n = 79) to 1.88 L at Endpoint (n = 69) compared with an increase from 1.65 L at baseline (n = 83) to 1. 77 L at Endpoint (n = 75) in subjects receiving fluticasone propionate 100 mcg 3

To interpret spirometry results, including Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC), consider the following:

• FEV1 measures the amount of air exhaled in one second, and a lower value may indicate obstructive lung disease.
• FVC measures the total amount of air exhaled, and a lower value may indicate restrictive lung disease.
• The FEV1/FVC ratio is also important, as a lower ratio may indicate obstructive lung disease.
• Spirometry results should be compared to predicted values based on age, sex, and height to determine if lung function is normal or abnormal.
• Prebronchodilator and postbronchodilator results can help determine if a patient has reversible airway obstruction. Key points to consider when interpreting spirometry results include:
• Obstructive lung disease: characterized by a low FEV1/FVC ratio.
• Restrictive lung disease: characterized by a low FVC.
• Reversible airway obstruction: characterized by an improvement in FEV1 after bronchodilator administration. It is essential to consider these factors and the individual patient's clinical context when interpreting spirometry results.

From the Research

Interpreting Spirometry Results

To interpret spirometry results, including Forced Expiratory Volume in 1 second (FEV1) and Forced Vital Capacity (FVC), follow these steps:

• Determine the validity of the test, considering patient effort and cooperation, as well as the interpreter's knowledge of appropriate reference values 4
• Identify the ventilatory pattern as obstructive or restrictive, and grade its severity if a pattern is identified 4
• Use predicted values and define abnormality based on the lower limit of normal (LLN), which is typically the 5th percentile of a healthy, non-smoking population 5

Key Parameters

Key parameters to consider when interpreting spirometry results include:

• FEV1: the volume of air exhaled in 1 second
• FVC: the total volume of air exhaled
• FEV1/FVC ratio: the ratio of FEV1 to FVC, which can indicate air-flow obstruction if less than 0.70 5
• However, using a fixed 0.7 cut-off value for the FEV1/FVC ratio may not be accurate, as it does not account for age-related changes 6

Predicted Values and Abnormality

When selecting predicted values, consider the patient's ethnic origin to avoid erroneous interpretation 7

• Defining abnormal values is critical, and a statistically valid definition of the lower limits of normal is recommended over a fixed percentage of the predicted value 5, 7
• The use of Global Lung Function Initiative (GLI) normal values may result in overdiagnosis of lung disease in certain populations, such as the Western Indian adult population 6

Clinical Application

Spirometry must be interpreted in conjunction with clinical information, including results of other investigations 7

• Salbutamol, a short-acting β2 agonist bronchodilator, can be effective in patients with mixed obstructive and restrictive pattern spirometry 8
• A systematic approach to interpretation, considering several important issues, is essential for meaningful and clinically useful interpretation of spirometry data 7