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Sputum cell profile: no help in occupational asthma

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Analysing the type of inflammatory cells in sputum does not help to confirm a diagnosis of occupational asthma in workers with borderline features of the condition. Asthma related to low molecular weight agents fell into eosinophilic and non-eosinophilic types but did not correlate with peak expiratory flow (PEF) response to exposure at work.

Examination of induced sputum from 38 consecutive workers with asthma related to low molecular weight agents showed that only 14 had sputum eosinophilia (eosinophils >2.2% of non-squamous cells). Grouping the workers according to whether they had sputum eosinophilia or not revealed that neutrophils were present in similar proportions in each group (mean (SD) 59.5 (19.6)% v 55.1 (18.8)%, respectively). Furthermore, no differences were apparent in diurnal variation in PEF and drop in PEF during work periods between the two groups. Other respiratory measures indicated that sputum eosinophilia correlated with more severe asthma and greater bronchodilator reversibility.

The researchers hypothesised that in asthma related to low molecular weight agents workers with small but consistent falls in PEF and whose diurnal variation in PEF was within normal values would have a neutrophilic, not an eosinophilic, inflammatory airway response and this could be used to corroborate the diagnosis. Such physiological behaviour in PEF by itself makes it difficult to decide whether to diagnose occupational asthma or not.

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