Comparison of Light and Electron Microscopy for Defining Occupational Asbestos Exposure in Transbronchial Lung Biopsies

Since asbestos burden in the lung can vary among areas, the usefulness of small tissue samples for identifying past occupational exposure is examined. Simulated transbronchial biopsy samples and open lung biopsy samples were collected from autopsy material from 12 former amosite asbestos workers and ten persons from the general population. Tissue evaluation included (1) paraffin embedment and light microscopy screening for fibrosis and ferruginous bodies, and (2) tissue digestion, which was analyzed by the combination of (A) light microscopy screening for ferruginous bodies and (B) electron microscopy (EM) screening for uncoated fibers. Using standard pathology techniques to classify the small samples was generally unsuccessful, the samples being too small or their size compounding other random sampling problems. The most reliable method of establishing which transbronchial biopsy tissue samples were from the occupationally exposed group occurred when light and EM analyses were used to evaluate digested tissue. The combined data from the EM analysis of two samples per subject indicated controls had two or fewer observed asbestos fibers, while the amosite asbestos workers had six or more fibers. This distinction was valid even in those who, 21 years before sampling, had worked for only a few weeks in the asbestos plant.