Pulmonary Function Tests:

Indications for pulmonary function tests (PFTs) have widened substantially, ranging from screening smokers for early lung disease to determining the diagnosis and prognosis of pulmonary conditions. Current indications also include screening for drug-induced lung toxicity and preoperative screening for lung resection surgery. In the workup of respiratory symptoms, such as dyspnea, cough, and wheezing, PFTs can identify obstructive or restrictive patterns that may suggest a diagnosis such as asthma or interstitial lung disease. The ratio of FEV1 to forced vital capacity is very sensitive to the presence of airflow limitation, although bronchoprovocation testing may be needed to diagnose asthma, especially in patients with mild intermittent disease. Measurements of lung volumes and carbon monoxide-diffusing capacity (DLCO) provide crucial information in selected patients. For example, a reduced DLCO may be a sign of more advanced disease, such as emphysema or pulmonary hypertension.Since the first description of the spirometer by John Hutchinson in the late 1800s, pulmonary function tests (PFTs) have expanded to include spirometry; lung volumes; carbon monoxide-diffusing capacity (DLCO) (transfer factor); respiratory muscle performance; and exercise and functional testing, such as the 6-minute walk test (6MWT) and cardiopulmonary exercise testing (CPET). Indications for PFTs have widened substantially, ranging from screening smokers for early pulmonary disease or screening patients for drug-induced lung toxicity to determining the diagnosis and prognosis of pulmonary conditions (Table 1). In this article, we will address the use of PFTs in common pulmonary diseases and the indications most relevant to the primary care practitioner. SCREENING Screening for obstructive lung disease in smokers.The significance of office spirometric screening for chronic obstructive pulmonary disease (COPD) in high-risk patients (such as persons who have smoked for more than 10 years) is well established. Spirometric signs of airway obstruction have been found in 24.3% of asymptomatic smokers compared with 14.4% of nonsmokers.1 The Lung Health Study showed that early intervention with smoking cessation in those identified to be at risk for COPD could modify disease progression.2 The Third National Health and Nutrition Examination Survey suggested that undiagnosed airflow obstruction was found in 12% of patients surveyed and was more common than physician-diagnosed COPD (3.1%) or asthma (2.7%).3 After adjusting for smoking, obesity, and comorbid conditions, the risk of impaired health and functional status with undiagnosed airflow obstruction was independently associated with the severity of forced expiratory volume in 1 second (FEV1) impairment.3 A consensus statement from the National Lung Health Education Program recommends that all patients aged 45 years and older who are current smokers and all patients with respiratory symptoms undergo office spirometry or diagnostic spirometry.4 There are no recommendations to perform screening PFTs for asymptomatic nonsmokers, because no studies have shown any advantage in doing so. Preoperative screening for lung disease. PFTs have a clear role in preoperative screening for lung resection surgery, but the role of PFTs in non-lung resection surgery is less clear. This is partly due to the lack of a unified definition of postoperative pulmonary complications in studies examining this role; the complex interaction of respiratory factors (obstructive or restrictive pulmonary disease, respiratory muscle weakness, smoking) and nonrespiratory factors (age, obesity, nutritional status, operative factors, proximity to diaphragm, type of anesthesia) affecting postoperative respiratory status; and the rapid pace of change in surgical techniques. The 1990 American College of Physicians' guidelines indicated that PFTs should not be done in patients without evidence of lung disease at physical examination who were to undergo nonthoracic surgical procedures.5 However, PFTs were recommended for patients with a history of tobacco use or