Is a previous diagnosis of asthma a reliable criterion for asthma–COPD overlap syndrome in a patient with COPD?

BACKGROUND: Some patients share characteristics of both COPD and asthma. As yet, there is no gold standard to identify patients with the so-called asthma–COPD overlap syndrome (ACOS). OBJECTIVE: To describe the differences between ACOS patients and the remaining COPD patients, and to compare the clinical characteristics of patients diagnosed with ACOS by two different criteria: previous diagnosis of asthma before the age of 40 years; and the diagnostic criteria of the Spanish guidelines of COPD. METHODS: Multicenter, observational, cross-sectional study performed in 3,125 COPD patients recruited in primary care and specialized outpatient clinics. Patients with COPD and a history of asthma before the age of 40 years were diagnosed with ACOS and compared to the remaining COPD patients. Subsequently, ACOS patients were subdivided based on whether they fulfilled the Spanish guidelines of the COPD diagnostic criteria or not, and they were compared. RESULTS: ACOS was diagnosed in 15.9% of the patients. These patients had different basal characteristics compared to the remaining COPD patients, including a higher frequency of women and more exacerbations despite lower tobacco exposure and better lung function. They were more likely to have features of asthma, such as a positive bronchodilator test, higher peripheral eosinophilia, and higher total immunoglobulin E. Within the ACOS group, only one-third fulfilled the diagnostic criteria of the Spanish guidelines of COPD; these individuals were not significantly different from the remaining ACOS patients, except for having more exacerbations and poorer lung function. CONCLUSION: ACOS patients diagnosed on the basis of a previous diagnosis of asthma differed from the remaining COPD patients, but they were similar to ACOS patients diagnosed according to more restrictive criteria, suggesting that a history of asthma before the age of 40 years could be a useful criterion to suspect ACOS in a patient with COPD.