Assessment of eosinophilic airway inflammation as a contribution to the diagnosis of occupational asthma

BackgroundAscertaining the presence of asthma through the assessment of nonspecific bronchial hyperresponsiveness (NSBH) is a key step in the diagnosis of occupational asthma (OA). We aimed at investigating whether indices of airway inflammation including fractional exhaled nitric oxide (FeNO) and sputum eosinophils would be useful adjuncts to the measurement of NSBH in diagnosing OA defined as a positive specific inhalation challenge (SIC). MethodsThe study included 240 consecutive subjects with a suspicion of OA who completed a SIC, of whom 133 showed a positive response. The sensitivity, specificity, and predictive values of NSBH, and FeNO, as well as sputum eosinophil counts assessed at baseline of the SIC were determined. ResultsA concentration of histamine inducing a 20% decline in FEV1 (PC20) 16 mg/mL showed a sensitivity of 87% and a specificity of 36%. A FeNO level 25 ppb and a sputum eosinophil count 2% provided lower sensitivity rates (47% and 39%, respectively) than the PC20 value. Eight of the 17 subjects without baseline NSBH despite a positive SIC showed a sputum eosinophil count 2%, a FeNO level 25 ppb, or both outcomes. Combining either a PC20 value 16 mg/mL or a FeNO 25 ppb increased the sensitivity to 91%. Using either a PC20 16 mg/mL or a sputum eosinophil count 1% increased the sensitivity to 94%. ConclusionAdding the assessment of FeNO level and sputum eosinophils to NSBH improves the identification of subjects who may have OA and require further objective testing before excluding the possibility of OA.