Diagnosing occupational asthma: use of induced sputum

The diagnosis of occupational asthma (OA) needs to be made with as much obj ective evidence as possible. If there is airway inflammation, measurement o f this should be an asset. The objective of this study was to investigate w hether there is an increase in induced sputum and blood eosinophils and eos inophil cationic protein (ECP) in OA after work exposure. Patients were assessed after a 2-4 week period at work and away from work w ith cell counts and ECP assays performed blind to the clinical data. They w ere considered to have OA if symptoms were worse at work and there was a fa ll in forced expiratory volume in one second (FEV1) greater than or equal t o 20% or in the provocative concentration of methacholine causing a 20% fal l in FEV1 (PC20) of four-fold or more compared with away from work, Patient s whose symptoms were worse at work but had a change in FEV1 of <20% and in methacholine PC20 of less than four-fold were considered as controls, Sixteen patients were studied, Ten had OA and six were controls. Patients w ith OA had a significant increase in median (interquartile range) sputum eo sinophils and ECP when at work compared with the periods out of work, 10.0 (17.05) versus 0.8 (1.6)% (p=0.007) aod 3,840 (6,076) verses 116 (180) mu g .L-1 (p=0.01). They also had a higher blood eosinophil count, 0.3 (0.5) x 1 0(9) versus 0.2 (0.1) x 10(9).L-1 (p=0.013), and a trend towards higher ser um ECP levels, 44.0 (20.0) versus 32.0 (18.5) mu g.L-1 (p=0.07). In conclusion, the proportion of eosinophils and levels of eosinophil catio nic protein in sputum are particularly high at work in patients with occupa tional asthma, suggesting that the measurement of these factors can supplem ent other physiological outcomes in establishing the diagnosis of occupatio nal asthma.