INTRODUCTION

The "classic" signs and symptoms of asthma are intermittent dyspnea, cough, and wheezing. Although familiar to most clinicians, these symptoms are nonspecific, making it sometimes difficult to distinguish asthma from other respiratory diseases. The diagnosis of asthma requires the history or presence of respiratory symptoms consistent with asthma, combined with the demonstration of variable expiratory airflow obstruction.

The tools used to diagnose asthma include history, physical examination, pulmonary function testing, and other laboratory evaluations. This topic review describes these tools, followed by several specific strategies for making the diagnosis of asthma in adolescents and adults. The information herein is consistent with "The National Asthma Education and Prevention Program (NAEPP): Expert Panel Report 3, Guidelines for the Diagnosis and Management of Asthma -- Full Report 2007" [1].

The diagnosis of asthma in children and older adults and an overview of asthma management are discussed separately. (See "Chronic asthma in children younger than 12 years: Evaluation and diagnosis" and "Diagnosis and management of asthma in older adults" and "An overview of asthma management".)

DEFINITION

Asthma has defied a precise definition acceptable to all disciplines. Part of the problem relates to the lack of specificity of the symptoms. Pathologically, asthma may be described broadly as "a chronic inflammatory disorder of the airways" [1]. However, this description omits the characteristic waxing and waning of airflow obstruction in asthma. A more useful definition would combine the central roles of inflammation and bronchial hyperresponsiveness with the characteristic clinical symptoms. As an example, asthma may be defined as “a common chronic disorder of the airways that is complex and characterized by variable and recurring symptoms, airflow obstruction, bronchial hyperresponsiveness, and an underlying inflammation. The interaction of these features of asthma determines the clinical manifestations and severity of asthma and the response to treatment [1].

The latter definition of asthma has features that overlap with the description of chronic obstructive pulmonary disease (COPD). Besides historic features (eg, onset in middle age and older, history of cigarette smoking), the characteristic that best distinguishes COPD from asthma is the degree of reversibility of airflow obstruction. In most instances the airflow obstruction of asthma is largely or completely reversible, while that of COPD is irreversible or incompletely reversible. (See 'Differential diagnosis' below and "Chronic obstructive pulmonary disease: Definition, clinical manifestations, diagnosis, and staging", section on 'Definitions'.)