Spirometry Values for Detecting a Restrictive Pattern in Occupational Health Settings

BACKGROUND: Pulmonary function tests are valuable measures for diagnosis and management of respiratory diseases. In the field of occupational medicine, spirometry is commonly performed, and in a considerable number of spirometries during occupational health evaluations, restrictive pattern is observed without any respiratory symptoms and may necessitate referral of the subject for body plethysmography, which is an expensive test. In this study, we evaluated the diagnostic accuracy of spirometry for detection of restrictive lung pattern in an occupational setting. MATERIALS AND METHODS: In a cross-sectional study from 2008 to 2012, 1224 subjects were selected and entered in the study out of 1,486 individuals referred for annual spirometry. Selected subjects underwent spirometry and body plethysmography. Subjects were divided into two groups of restrictive and non-restrictive patterns and then sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of spirometry for detection of restrictive lung pattern were calculated using total lung capacity measured by plethysmography as the gold standard. Receiver operating characteristic (ROC) curves were used as well. RESULTS: Spirometry showed sensitivity, specificity, PPV and NPV of 97.75%, 73.04%, 73.72% and 97.67% for FVC< lower limit of normal (LLN) and 98.68%, 78.00%, 77.31% and 98.83% for FVC< LLN along with FEV(1)/FVC≥ LLN, respectively. According to the ROC curve, the best cut-off point for FVC for detection of restrictive lung pattern was 70%. CONCLUSION: This study showed that spirometry is a useful method in occupational health evaluations to rule out restrictive lung patterns with acceptable accuracy; however, it is not an accurate tool for detection of restrictive lung pattern in an occupational setting. Simultaneous use of FVC and FEV(1)/FVC for detection of restriction increases the predictive value of spirometry.