Patients exposed to asbestos dust, even for a short time, may develop diseases many years later. Patients may have large numbers of asbestos fibres, but no asbestos bodies; few fibres or bodies but severe fibrosis or mesothelioma; or large numbers of asbestos bodies, but little evidence of fibrosis, etc. Some types of asbestos appear to be more likely to cause mesothelioma than other types.
Asbestos is a silicate and consequently will polarize light, however, the fibres can be very fine and easily overlooked by the inexperienced. After a period of time, the ends of the fibres are coated by an iron containing protein material, producing the classical "dumbell" shape. Additional protein-iron material will produce a fully coated fibre. Coated fibres are no longer birefringent when viewed by polarized light.
Asbestos bodies are strongly Perls' Prussian blue positive due to the ferric iron present in the coating. However, the morphology of the asbestos body is unmistakable and does not usually require confirmation by special stains.
Some texts have recommended using microincineration to destroy the cellular tissue components and leave a residue of asbestos containing ash that can be examined. This method is unreliable, time consuming and generally inconvenient.
The following technique was developed in Nottingham, England for a research project during the early 1970's, hence the name.
Asbestos fibres or bodies can be detected in both fresh and fixed tissues.
Slice through a large portion of lung tissue (the left lower lobe is suitable) to expose the parenchyma. Squeeze the tissues very firmly to extract the tissue fluids. Using a funnel to collect them into a large plastic centrifuge tube is most convenient. This is a messy, bloody, seemingly crude procedure, but it works very well. Add a lysing reagent to the fluid to get rid of the red cells, saponin is suitable, but any lysing agent will work. Centrifuge the tissue fluid, discard most of the supernatent and make wet preparations from the concentrate. No staining is required. Asbestos bodies, if present, are very conspicuous and easily identified. Asbestos fibres, much finer and easily overlooked, can be identified by the use of polarized light. The wet preparations are not permanent and can be discarded after examination. The lung tissue must be unfixed. Autolysis and putrefaction do not have any effect on the asbestos content, although they make the procedure less pleasant.
From each processed block of lung tissue, cut a 30 micron section. Dry as usual, dewax, coverslip, and examine using brightfield and polarized light microscopy. Asbestos fibres or bodies are easily identified. The section does not require staining.
Internet communication, Kamloops, BC, Canada
Last updated January 2019