Spirometry is the gold standard for diagnosing airflow obstruction and monitoring its progression. Valid spirometry requires a standardized approach based on guidelines. A presentation during the ACAAI annual meeting updated allergists on the latest American Thoracic Society (ATS) guidelines regarding the procedure, and offered tips for reliable, high-quality results.
Mario Castro, MD, MPH, of the Washington University School of Medicine in St. Louis, explained that spirometry measures the rate at which the lung changes volumes during forced breathing maneuvers. A patient takes a full inhalation, followed by a forced exhalation to rapidly empty the lungs, which lasts for as long as possible or until a plateau.
According to the National Lung Health Education Program, spirometry is used for patients > 45 years old who report smoking to detect chronic obstructive pulmonary disease (COPD), as well as people with respiratory symptoms such as chronic cough, sputum, wheezing, or dyspnea on exertion. The procedure also is indicated when clinicians are trying to diagnose pulmonary disease in patients with history of pulmonary symptoms, physical findings, or abnormal laboratory results. Castro added that spirometry also has an important role in assessing severity and progression of disease or evaluating preoperative risks, and is a useful tool for objective measurement of disability and impairment
Interpreting spirometry results involves flow-volume curves. Clinicians should examine the curves, the FEV1/FVC ratio, and the FEV1 value. Of note, ATS guidelines recommend that “values such as forced inspiratory flow at 75% of FVC (FEF75%) and FEF 25–75% have not demonstrated added value for identifying obstruction in adults or children, and therefore are not recommended for routine use.”
Castro illustrated the flow curves of normal, obstructive, and restrictive spirometry results to help attendees recognize the patterns. He also offered tips for clinicians to achieve the most accurate and reproducible results.
- Perform daily spirometer calibration checks.
- Measure a patient’s height accurately (without shoes) prior to the first test.
- Explain the test and demonstrate the maneuver.
- Coach patients to achieve maximal inhalation, explaining that they should “blast out” air, blowing out for at least six seconds.
The goal is to achieve at least three acceptable and reproducible results. If that is not possible after eight attempts, clinicians should stop, Castro said. The reasons spirometry should be repeated include: a test when the patient has a hesitating start, which shows as two peaks; a test when the patient lacks maximal effort, which shows as variability in peaks among repeated studies; and a test when the patient quits too soon. Patients often report that because of cough, “the test can feel like a workout for them,” which can alter results.
Also, he cautioned physicians about normative values. Most normative values were stablished based on a less diverse population of middle-aged patients. However, patient populations are increasingly diverse, and normative values should be based on race/ethnicity, height to the nearest centimeter, age to one decimal place, and gender. “Pay attention to where your normative values are coming from,” he said. “Erroneous decisions can be made when estimates based on middle-aged adults are used on older patients.”
Castro referred the audience to the ATS Recommendations for a Standardized Pulmonary Function Report, published in the American Journal of Respiratory and Critical Care Medicine in 2017 (Culver, et al.), which provides acceptability criteria for spirometry on an A–F grading scale. To achieve high grades, he recommended that offices have one or two staff members who stay up to date on guidelines and equipment.