Forced vital capacity test protocol

Am Fam Physician. 2020;101(6):362-368

Author disclosure: No relevant financial affiliations.

High-quality, office-based spirometry provides diagnostic information as useful and reliable as testing performed in a pulmonary function laboratory. Spirometry may be used to monitor progression of lung disease and response to therapy. A stepwise approach to spirometry allows for ease and reliability of interpretation. Airway obstruction is suspected when there is a decreased forced expiratory volume in one second/forced vital capacity (FEV₁/FVC) ratio, but there is no strong evidence to clearly define what constitutes a significant decrease in this ratio. A low FVC is defined as a value below the 5th percentile in adults or less than 80% of predicted in children and adolescents five to 18 years of age. The FEV₁/FVC ratio and FVC are used together to identify obstructive defects and restrictive or mixed patterns. Obstructive defects should be assessed for reversibility, as indicated by an improvement of the FEV₁ or FVC by at least 12% and 0.2 L in adults, or by more than 12% in children and adolescents five to 18 years of age after the administration of a short-acting bronchodilator. FEV₁ is used to determine the severity of obstructive and restrictive disease, although the values were arbitrarily determined and are not based on evidence from patient outcomes. Bronchoprovocation testing may be used if spirometry results are normal and allergen- or exercise-induced asthma is suspected. For patients with an FEV₁ less than 70% of predicted, a therapeutic trial of a short-acting bronchodilator may be tried instead of bronchoprovocation testing.

Approximately 1% to 4% of all visits to primary care offices are for dyspnea. 1 The proper use of pulmonary function tests can help differentiate many of the causes of dyspnea, monitor the progression of chronic pulmonary disease, and assess response to treatment. In a cross-sectional study, primary care physicians underestimated the severity of chronic obstructive pulmonary disease (COPD) in 41% of patients and overestimated severity in 29% of patients when compared with immediate, in-office spirometry. Overall, physician rating of severity was accurate in only 30% of patients. 2 Spirometry is recommended as part of the diagnostic workup in patients with presumed COPD or asthma by the American Thoracic Society/European Respiratory Society (ATS/ERS) 3 ; the Global Initiative for Chronic Obstructive Lung Disease (GOLD) 4 ; the Global Initiative for Asthma 5 ; and the American Academy of Allergy, Asthma, and Immunology. 6 High-quality spirometry performed in a family physician's office is comparable to testing performed in a pulmonary function laboratory. 7 , 8 A video of office-based spirometry is available at https://bit.ly/2JAIYGx. Although there are different types of pulmonary function tests, this article focuses on office-based spirometry.