Reliability of Pulmonary Function Tests in Patients with Chronic Obstructive Pulmonary Disease

Introduction: Chronic Obstructive Pulmonary Disease (COPD) is frequently underdiagnosed due to limited use and suboptimal quality of spirometry. Methods: This multicenter, prospective observational study aimed to assess the quality of spirometry tests in COPD patients across six tertiary care centers in Turkey. A total of 560 spirometry tests were independently evaluated by two pulmonologists, and inter-rater reliability was analyzed using Cohen’s Kappa. Results: The study included 124 women and 436 men, with a mean age of 65.9± 10.2 years. Spirometry patterns were interpreted as obstructive in 79.1% of tests, restrictive in 5.7%, mixed in 2.7%, normal in 6.7%, inconclusive in 5.5%, and as upper airway obstruction in 0.18% of cases ( K =0.890). Routine post-bronchodilator testing was performed in 87.14% of the cases, while 12.85% were post-reversibility tests. Graphical data included volume-time curves (88.5%), flow-volume loops (99.6%), and inspiratory limbs (98.7%). Reference values were predominantly based on ECSC (86.4%), followed by GLI (8.9%) and NHANES (0.25%). Mean spirometric values included FEV1 (% predicted) 57.2%, FVC (% predicted) 72.7%, and FEV1/FVC 61.9%. Cough in the first second of FVC was observed in 17 (3%) ( K =0.677), variable or insufficient effort 13.4% ( K =0.563), mouth leak 1.8% ( K =0.305), mouthpiece obstruction 0.5% ( K =0.332), rapid expiration 1.8% ( K =0.354), increased concavity 83% ( K =0.683), and small airway obstruction 87% ( K =0.709) were reported by interpreters. Conclusion: Spirometry reports frequently lack key information such as preliminary diagnoses, test indication, technician, and device details. ECSC is the most commonly used reference. Rates of inconclusive and erroneous tests—due to variable or insufficient effort, mouth leak, mouthpiece obstruction, and rapid expiration—are low. Keywords: chronic obstructive pulmonary disease, COPD, pulmonary function tests, spirometry