Clinical characteristics of patients newly diagnosed with COPD by the fixed ratio and lower limit of normal criteria: a cross-sectional analysis of the TargetCOPD trial
Received 21 July 2017
Accepted for publication 21 September 2017
Published 21 June 2018 Volume 2018:13 Pages 1979—1986
Checked for plagiarism Yes
Review by Single-blind
Peer reviewer comments 3
Editor who approved publication: Dr Richard Russell
Martin R Miller,1 Shamil Haroon,1 Rachel E Jordan,1 Alice J Sitch,1 Andrew P Dickens,1 Alexandra Enocson,1 David A Fitzmaurice,2 Peymané Adab1
1Institute of Applied Health Research, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham, UK; 2Warwick Clinical Trials Unit, Warwick Medical School, University of Warwick, Coventry, UK
Background: Consensus on the definition of airflow obstruction to diagnose COPD remains unresolved.
Methods: We undertook systematic case finding for COPD in primary care using the fixed ratio (FR) criterion (forced expiratory volume in 1 s/forced vital capacity [FEV1/FVC] <0.7) for defining airflow obstruction and also using the lower limit of normal (LLN). We then compared the clinical characteristics of those identified by the 2 criteria.
Results: A total of 3,721 individuals reporting respiratory symptoms were invited for spirometry. A total of 2,607 attended (mean age 60.4 years, 52.8% male, 29.8% current smokers) and 32.6% had airflow obstruction by FR (“FR+”) and 20.2% by LLN (“LLN+”). Compared with the LLN+/FR+ group, the LLN–/FR+ group (12.4%) was significantly older, had higher FEV1 and FEV1/FVC, lower COPD assessment test scores, and less cough, sputum, and wheeze, but was significantly more likely to report a diagnosis of heart disease (14.2% versus 6.9%, p<0.001). Compared with the LLN+/FR+ group, the LLN–/FR– group was younger, had a higher body mass index, fewer pack-years, a lower prevalence of respiratory symptoms except for dyspnea, and lower FVC and higher FEV1. The probability of known heart disease was significantly lower in the LLN+/FR+ group compared with those with preserved lung function (LLN–/FR–) (adjusted odds ratio 0.62, 95% CI: 0.43–0.90) but this was not seen in the LLN–/FR+ group (adjusted odds ratio 0.90, 95% CI: 0.63–1.29).
Conclusion: In symptomatic individuals, defining airflow obstruction by FR instead of LLN identifies a significant number of individuals who have less respiratory and more cardiac clinical characteristics.
Keywords: lower limit of normal, diagnostic criteria, primary care
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