Abstract

Background
Bronchial responsiveness and IgE-mediated reactivity are associated with specific bronchial reactivity to allergens.

Objective
Our aim was to examine whether airway inflammation also plays a role.

Methods
Retrospective analysis of all subjects who underwent specific inhalation challenges in the investigation of occupational asthma (OA) since 2000. Responsiveness to methacholine (PC20) and levels of eosinophils and neutrophils in induced sputum on the control day were associated with the presence of OA (positive-specific inhalation challenge). In a sample of subjects exposed to wheat flour, we also examined the role of specific IgE-mediated reactivity (skin reactivity, specific IgE).

Results
PC20 level was significantly more often normal in subjects with OA (35 of 129, 27% instances) by comparison with non-OA (15 of 189, 8% instances), but the positive predictive value of responsiveness to methacholine for OA was low (35%). Coupling information on the level of eosinophils to responsiveness to methacholine increased positive predictive values for OA from 39% to 69% depending on the thresholds used. The best balance of positive (69%) and negative (60%) predictive values was obtained in the case of normal PC20 and eosinophils 3%. In a multivariate analysis carried out in 34 subjects exposed to wheat flour, responsiveness to methacholine, sputum eosinophils, skin weal size and levels of specific IgE were all significantly associated with OA to wheat flour.

Conclusion and Clinical Relevance
Information on the level of sputum eosinophils in addition to PC20 provides a better association with OA vs. non-OA when PC20 is normal. Levels of sputum eosinophils in addition to PC20 and IgE-mediated reactivity increase the likelihood of OA due to wheat flour

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Comments

This is an interesting paper, but all the analysis is retrospective and requires prospective validation. Although there was a relationship between sputum eosinophilia, NSBR and occupatiuonal asthma both together and separately, the negative combination is not enough to exclude occupational asthma (negative predictive value 58% when compared with non-occupational asthma. There is no particular reason why NSBR or sputum eosinophilia should be diffeent in occupational and non-occupational asthma. If non-asthmatics are include the negative predictive value is higher. It shows that there are workers with challenge positive occupational asthma where both the NSBR and sputum eosinophils are normal when investigated a median 76 days after last exposure (Interquartile range 1 to 173, showing at least 25% were currently exposed at the time of the challenge). Median interval from last exposure to challenge 76 days. 65/129 with OA had sputum eosinophils <1%; 37/129 >3%. NSBR normal (>16mg/ml) in 35/129 with OA (27%). Positive prictive value of OA for eosinophils >1% 44% and >3% 49%. Negative predictive value of OA versus non-OA 58% for spuum eosinohils <1% and 30% for NSBR >16mg/ml. Negative predictive value of Pc20 >16mg/ml and eosinophils <1% 58% against non-occupational asthma.

4/2/2011