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Comparing the different diagnostic criteria of Asthma‐COPD overlap

To the Editor, Asthma and chronic obstructive pulmonary disease (COPD) are both airway diseases with often similar clinical manifestations despite having different pathophysiologies. Asthma‐COPD overlap (ACO) is a condition characterized by overlapping clinical features of both diseases in patients. There are some clinical situations suggestive of ACO as follows. First, childhood asthma is regarded as an independent risk factor for COPD, especially when accompanied by smoking. Second, some patients with COPD show significant improvements in their forced expiratory volume in 1 second (FEV1) following the use of a bronchodilator. 2 Third, as many as 30%‐40% of patients with COPD shows signs of eosinophilic inflammation either in their blood or sputum. Although ACO was recently recognized, it remains a question whether it is a single disease entity distinguishable from asthma and COPD. This can be attributed to the exclusion of patients with both asthma and COPD features from clinical studies on asthma and COPD and to the lack of a consensus for ACO diagnosis. As the diagnostic criteria proposed for ACO by the global initiative for asthma (GINA) and the global initiative for chronic obstructive lung disease (GOLD) are difficult to use in clinical practice, several studies proposed their own diagnostic criteria. Here, we compare the prevalence, clinical features, exacerbation risk, and diagnostic agreement between different diagnostic criteria in a well‐designed prospective, multicentre cohort in Korean patients with COPD. The Korean COPD subgroup study (KOCOSS) cohort is a prospective, ongoing cohort to clarify the phenotype of COPD. Patients with COPD in 48 tertiary referral hospitals in Korea were enrolled and this cohort was registered at www.clinicaltrials.gov (NCT02800499). The inclusion criteria for this cohort included adults aged ≧40 years and postbronchodilator FEV1/forced vital capacity (FVC) <70%. Patients were followed up at least every 6 months and exacerbation data were recorded on every visit. Moderate exacerbation was defined as an exacerbation that led a visit to an outpatient clinic earlier than scheduled with a prescription of systemic steroids and/or antibiotics, while severe exacerbation was defined as an exacerbation that led to a visit to the emergency department or hospitalization. The ACO study was initiated at the Korean Academy of tuberculosis and respiratory disease by the asthma study group and was conducted prospectively on KOCOSS registered patients who were willing to participate. Questionnaires for ACO were administered between July 2016 and October 2016 and 635 patients were enrolled. We selected four diagnostic criteria for ACO including the GINA/ GOLD, ATS roundtable, modified Spanish, and updated Spanish COPD guidelines. Each item of these four criteria and the criteria of the ACO diagnosis are described in Table 1. In addition to the four mentioned criteria, questionnaires were provided to pulmonology specialists at each of the hospitals included for ACO diagnosis based on their clinical judgment by questionnaire “Is this patient likely to be classified with ACO?” (Table 1 and Figure S1). We analyzed patients who could distinguish ACO from non‐ACO except missing data. The risk of exacerbation during the 6‐month follow‐up was analyzed using Cox proportional hazards analysis, and the incidence of exacerbation was analyzed using negative binomial regression model. Cohen's kappa values were used to assess the diagnostic consistency between the different diagnostic criteria. The GINA/GOLD criteria were used as the gold standard, and the degree of similarities between criteria was analyzed by a receiver operating characteristic (ROC) curve. Among 635 patients included in ACO questionnaires, 18 of 493 (3.6%), 98 of 628 (15.6%), 86 of 570 (15.1%), and 135 of 435 (31.0%) met the ACO criteria for the ATS roundtable, GINA/ GOLD, modified Spanish COPD, and updated Spanish COPD guidelines, respectively (Table 1 and Figure S2). In addition, 168 of 571 patients (29.4%) were identified as ACO according to specialists’ diagnosis. Various clinical characteristics, lung function, and laboratory results of patients with ACO were compared with non‐ACO COPD patients were shown in Tables S1 and S2. As expected, reversible airflow limitation on postbronchodilator pulmonary function test was more common in ACO patients across all diagnostic criteria and ICS was more frequently prescribed to ACO patients. ACO patients tend to had higher scores on quality of life questionnaires than non‐ACO patients (COPD assessment test score was 17.2 ± 8.5 vs 14.8 ± 7.8 and 18.8 ± 8.3 vs 15.0 ± 7.7 in those diagnosed according to specialists and GINA/GOLD criteria as ACO and non‐ACO COPD, respectively). Several asthmatic clinical features in ACO and non‐ ACO patients are presented in Table S2. At the 6‐month follow‐up, 574 of 635 patients were included in the exacerbation analysis and moderate‐to‐severe exacerbation occurred in 89 patients (15.5%) with a mean frequency of 0.24 ± 0.69 events. There was no significant difference in the exacerbation and the incidence risk of exacerbation between ACO and non‐ACO patients across all four diagnostic criteria even after adjusting for multiple covariates (Table S3). Received: 3 July 2018 | Revised: 6 August 2018 | Accepted: 26 August 2018 DOI: 10.1111/all.13577