IntroductionThe National Health and Nutrition Assessment Survey (NHANES) is being adopted for interpreting spirometry in occupational examinations. Rubber workers have an elevated risk of respiratory health issues due to industrial exposure, and changes in the equations would affect spirometry monitoring programs.ObjectiveTo determine the differences in the use of the Knudson and NHANES III equations in nonsmoking workers in the rubber industry.MethodA cross-sectional study was conducted with 75 nonsmoking workers with occupational exposure to rubber for at least two years. The factory had engineered protection controls and provided respiratory protection to the workers. Spirometry was conducted according to Spirometry Testing in Occupational Health Programs and Standardization of Spirometry: American Thoracic Society/European Respiratory Society.ResultSpirometric prediction differences were present in the restrictive pattern assessment based on forced vital capacity (FVC), in which three individuals (4%) classified as normal according to Knudson presented restrictive disease according to NHANES III; only in the record of one participant was there restrictive disease using both equations. There was an 8% discrepancy for small airway obstruction in which six workers classified as normal using NHANES III were classified as diseased (FEF 25–75 <50%) using the Knudson equation.ConclusionIn the respiratory examination of workers exposed to rubber, the NHANES III equation is better able to detect restrictive diseases than is the Knudson equation; however, the Knudson equation is more sensitive to obstructive patterns.