Clinical Utility of Additional Measurement of Total Lung Capacity in Diagnosing Obstructive Lung Disease in Subjects With Restrictive Pattern of Spirometry.

BACKGROUND Total lung capacity (TLC), forced expiratory flow between 25 and 75% (FEF25-75%), peak expiratory flow (PEF), or post-bronchodilator volume response is recommended to detect obstructive abnormalities in the lung. The present study was performed to evaluate the usefulness of these pulmonary function test (PFT) parameters to diagnose obstructive lung disease in subjects with a restrictive pattern of spirometry. METHODS A retrospective study was conducted in 64 subjects with a restrictive pattern of spirometry (normal FEV1/FVC and low FVC) out of 3,030 patients who underwent all pre- and post-bronchodilator spirometry and lung volume measurement between April 2008 and December 2010. After subjects were clinically classified into those with obstructive lung disease, restrictive lung disease, and mixed lung disease, the agreements between the clinical diagnosis and PFT classification according to TLC, FEF(25-75%), PEF, and post-bronchodilator response criteria were compared. RESULTS Of 64 subjects, 18 (28.1%) were classified with obstructive lung disease, 39 (60.9%) had restrictive lung disease, 1 (1.6%) had mixed lung disease, and 6 (9.4%) had no clinical lung disease. Among the 58 subjects with clinical lung disease, 22 (37.9%), 37 (63.8%), 33 (56.9%), and 3 (5.2%) were classified as having obstructive pattern based on TLC, FEF25-75%, PEF, and post-bronchodilator response criteria, respectively. The kappa coefficients for the agreement between the clinical classification and PFT classification using TLC, FEF25-75%, PEF, and post-bronchodilator response criteria in 58 subjects were 0.59, 0.18, 0.17, and < 0.01, respectively. CONCLUSIONS The additional measurement of TLC is more useful than FEF25-75%, PEF, and post-bronchodilator response for diagnosis of obstructive lung disease in subjects with a restrictive pattern of spirometry, when obstructive lung disease is clinically suspected.