Asthma and chronic obstructive pulmonary disease (COPD) affect more than 40 million Americans,^1,2 and together these two diseases contribute to more than $100 billion in annual health costs in the United States.^3,4 In 2020, more than 4,000 Americans died of asthma, including at least 200 children,⁵ and more than 150,000 Americans die from COPD each year,⁶ making chronic lower respiratory disease the fourth-leading cause of death in the United States.⁷

Across the spectrum of obstructive lung disease, overlap has long been known to occur.^8,9 Clinically, asthma and COPD coexist in many patients who demonstrate increased variability of airflow and incomplete reversibility of airway obstruction.¹⁰ Nearly 20% of patients with obstructive lung disease report having more than one lung condition, and this percentage increases with age.¹¹

A new syndrome, asthma-COPD overlap, emerged in the early 2000s, with 15% to 45% of patients who have obstructive lung disease potentially qualifying for the distinction.¹² However, major guidelines currently state that any reference to an overlap syndrome is a simple descriptor for patients who have features of both asthma and COPD and that the term does not refer to a specific disease entity.¹³ Physicians are encouraged to consider asthma and COPD as different disorders that share some common traits and clinical features and may coexist in an individual patient.¹⁴

This case-based review focuses on the distinguishing characteristics of asthma and COPD and presents a classic example of asthma-COPD overlap. Previous articles in American Family Physician discuss indications for and interpretation of office spirometry ¹⁵ and also interpretation of pulmonary function tests.¹⁶ It is important to note that Choosing Wisely guidelines recommend that physicians do not diagnose or manage asthma or COPD without spirometry.^13,14,17,18 For a full review of evidence-based treatment guidelines, refer to the National Heart, Lung, and Blood Institute’s Expert Panel recommendations, updated in 2020¹⁷; the Global Initiative for Asthma guidelines, updated in 2022¹³; and the Global Initiative for Chronic Obstructive Lung Disease guidelines, updated in 2023.¹⁴

Case 1

A 42-year-old woman with a 12-month history of mild shortness of breath associated with some intermittent wheezing during upper respiratory tract infections presents for a follow-up visit. She does not smoke. She was not diagnosed with asthma as a child but used inhalers before physical education class and has a history of atopic dermatitis and allergic rhinitis. Office spirometry reveals a reduced forced expiratory volume in one second/forced vital capacity (FEV₁/FVC) ratio of 77%, with FEV₁ improvement of 17.4% after a bronchodilator is given (Figure 1).

Asthma is a heterogenous disease with respiratory symptoms such as wheezing, shortness of breath, chest tightness, cough, and reduced expiratory lung function on spirometry that varies over time and in intensity.¹³ Risk factors for asthma include preterm birth, having respiratory symptoms since childhood, family history of asthma or allergies, personal history of allergic rhinitis or eczema, tobacco exposure, and obesity.¹³

Spirometry is central to distinguishing between asthma and other forms of obstructive lung disease.^13,15 However, people with asthma often have normal lung function in the absence of an exacerbation, making a diagnosis on the first attempt challenging. If clinical suspicion for asthma or COPD is high despite normal results on initial spirometry, it is reasonable to repeat spirometry later. If the FEV₁/FVC ratio is reduced on initial spirometry, it suggests an obstructive process, and a bronchodilator response should be tested. Substantial reversibility after bronchodilator use, defined as an increase in FEV₁ of greater than 12% and greater than 200 mL, is consistent with asthma.^13,17 A nonreversible or only mildly reversible obstructive pattern suggests an alternate diagnosis and may lead to additional evaluation.¹⁹