ELECTRON-MICROSCOPIC MICROANALYSIS OF BRONCHOALVEOLAR LAVAGE - A WAY TO IDENTIFY EXPOSURE TO SILICA AND SILICATE DUST

Objectives-The diagnostic implications of finding non-fibrous inorgani c particles in bronchoalveolar lavage (BAL) fluid has not been fully a ssessed. The aim of this study has been to measure the silica and non- fibrous silicates in BAL fluid from populations with different exposur es to inorganic dust, and to find whether such measurement is useful f or diagnostic purposes. Materials and methods-BAL samples from 19 subj ects with only environmental exposure to inorganic dust (group A, mean (SD) age 50.7 (15.2)), 23 subjects with normal chest x ray films expo sed to silica or silicates at work (group B, mean (SD) age 52.0 (12.4) ), and 15 subjects with a previous diagnosis of silicosis (group C, me an (SD) age 68.0 (6.5)) were studied. Absolute and relative cell count s were found, and the samples were prepared for microanalysis by elect ron microscopy (EM). Firstly, semiquantitative x ray microanalysis was performed to find the level of silicon (Si) (peak/background Si) and this was followed by microanalysis of individual particles by EM. Vari ables related to the level of Si detected were assessed with multivari ate analysis. Results-Detected levels were higher in group B (2.09, 95 % confidence interval (95% CI) 1.56 to 2.82) and C (1.50, 95% CI 1.07 to 2.12) than in group A (0.87, 95% CI 0.66 to 1.16) (P<0.05, Dunett t test). A first multivariate analysis showed that exposure to silica o r silicates was the only determinant of the level of Si expressed as l og peak/background Si, when adjusted for age, sex, smoking habit, and cell count. A second multivariate analysis with microanalysis of indiv idual particles as an independent variable showed the silica count to be the main predictor of detected concentration of Si. Silica and non- aluminium silicates together explain 55.5% (R-2) of the variation in d etected levels of Si. Conclusions-Detected levels of Si in BAL fluid d epend on silica count and are higher in subjects with exposure to inor ganic dust at work, but will not discriminate between exposed subjects with and without silicosis. Because semiquantitative x ray microanaly sis does not accurately define exposure to non-silica inorganic partic les, this measurement must be followed by EM microanalysis of individu al particles in most cases, especially when exposure to silicates or m etal dust is suspected.