Clinical characteristics of patients newly diagnosed with chronic obstructive pulmonary disease by the fixed ratio and lower limit of normal criteria: a cross-sectional analysis of the TargetCOPD trial

Consensus on the definition of airflow obstruction to diagnose COPD remains unresolved. We undertook systematic case finding for COPD in primary care using the fixed ratio (FR) criterion (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 two criteria. 3721 individuals reporting respiratory symptoms were invited for spirometry. 2607 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 to the LLN+/FR+ group, the LLN-/FR+ group (12.4%) was significantly older, had higher FEV1 and FEV1/FVC, lower CAT scores, and less cough, sputum and wheeze, but were significantly more likely to report a diagnosis of heart disease (14.2% vs 6.9%, p<0.001). Compared to the LLN+/FR+ group, the LLN-/FR- group were younger, had a higher BMI, fewer pack-years, a lower prevalence of respiratory symptoms except for dyspnoea, and had lower FVC and higher FEV1. The probability of known heart disease was significantly lower in the LLN+/FR+ group compared to those with preserved lung function (LLN-/FR-) (adjusted odds ratio 0.62 (95% CI 0.43 to 0.90) but this was not seen in the LLN-/FR+ group (adjusted OR 0.90, 95% CI 0.63 to 1.29). 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.