Table 7.1.5.

Lung asbestos fibre counts per gram of dried lung

	Light microscopy	Electron microscopy
Normal city dwellers	Up to 50 000	Up to 5 000 000
Mesothelioma	Over 20 000	Over 1 000 000
Asbestosis (minimal)	Over 100 000	Over 10 000 000
Asbestosis (established)	Over 1 000 000	Over 100 000 000

The light microscopic counts include total fibres (coated and uncoated). The electron microscopic counts include only amphibole asbestos. Results from different laboratories vary and these figures, derived from several sources,216, 231, 232 provide only a general guide. Reliable results depend upon counts being made regularly and the normal range from that laboratory being ascertained. Ratios of counts obtained by electron and light microscopy vary greatly but approximate to 100.