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

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.