Aims: To assess the misclassification of chronic obstructive pulmonary disease (COPD) in Australian primary care.
Methods: A cross-sectional study was performed in 31 (19%) practices in one Australian state. 341 patients with COPD (database diagnosis or current use of tiotropium plus GP confirmation) completed spirometry and questionnaires. Predictors of misclassification were investigated with multi-level mixed-effects logistic regression allowing for clustering by practice.
Results: Spirometric confirmation of COPD (forced expiratory volume in 1 s/forced vital capacity (FEV1/FVC) ratio <0.7) was not present in 107 (31%) patients; 60 (56%) had normal lung function, seven (7%) had scalloped flow-volume curves and FEV1 <80% predicted, 40 (37%) had restriction (FVC <80% predicted). Among 107 misclassified patients the bronchodilators used were tiotropium in 26% and long-acting β2-agonists in 22%. The likelihood of misclassification increased with overweight/obesity (odds ratio (OR) 2.66; 95% CI 1.50 to 4.70) and self-reported allergic rhinitis/hay fever (OR 1.72; 95% CI 1.13 to 2.64) after adjustment for age, gender, and smoking.
Conclusions: Symptom-based diagnosis of COPD in primary care is unreliable, especially if patients are overweight, so diagnostic spirometry is essential to avoid inappropriate management.