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Changes in sputum cell counts after exposure to occupational agents: what do they mean?

BACKGROUND
Exposure to occupational agents can induce eosinophilic inflammation in subjects with occupational asthma (OA). It might also induce nonspecific changes in airway inflammation in subjects without OA.


OBJECTIVES
We sought to investigate the changes in airway inflammation induced by exposure to occupational agents in subjects with and without OA and to determine which changes in sputum eosinophil numbers and bronchial responsiveness to methacholine should be regarded as clinically significant for predicting a 20% fall in FEV(1).


METHODS
We performed specific inhalation challenges (SICs) in 3 groups of subjects: subjects reporting a history consistent with OA with a positive SIC response (n = 17); subjects reporting a history consistent with OA with a negative SIC response (n = 14); and asthmatic subjects without any history of OA (n = 10). Induced sputum and methacholine challenges were performed at the end of the control day and again at the end of the last day of exposure; the last day of exposure was always performed in the laboratory.


RESULTS
There was an increase in median sputum eosinophil and neutrophil numbers in subjects with positive SIC responses. Cell counts remained unchanged after exposure in asthmatic subjects without OA. A combination of a greater than 0.26 10(6)/mL increase in sputum eosinophil numbers and a decrease in the concentration of methacholine inducing a 20% fall in FEV(1) of at least 1.8-fold compared with baseline values predicted a 20% fall in FEV(1) in 96% (95% CI, 70%-99%) of patients.


CONCLUSION
Exposure to occupational agents per se does not induce airway inflammation. Changes in both sputum eosinophil counts and methacholine responsiveness are satisfactory predictors of a significant bronchial responsiveness to occupational agents.