Fiber counting and analysis in the diagnosis of asbestos-related disease

Our plain-English summary of Fiber counting and analysis in the diagnosis of asbestos-related disease, by A. Churg (Human Pathology, 1982).

The study

• Author: A. Churg
• Journal: Human Pathology
• Published: 1982;13(4):381-92
• Cited by: 113 articles, as counted by NIH iCite
• Read it: PubMed · Publisher
• In J-M's library: Johns-Manville's company medical library held a copy (J-M no. 001776).

Abstract

Analysis of numbers and types of asbestos fibers present in lung tissue may provide insights into the pathogenesis of asbestos-induced disease, as well as diagnostic information concerning the relationship of a given lesion to asbestos exposure. This type of analysis requires extraction of fibers and asbestos bodies from lung tissue, preferably by means of a digestion-and-concentration technique, and examination with a combination of electron optical techniques, including electron diffraction and energy-dispersive x-ray spectroscopy. The combination permits definitive identification of asbestos fibers. Asbestos bodies have been shown to contain asbestos no matter what population they are found in, but they appear to be of value in ascertaining unusual exposure only when present in very large numbers. Numbers of asbestos bodies markedly underestimate total numbers of fibers present in lung. In patients from the general population, the mean number of asbestos fibers is about 1 X 10(6)/g dry lung; of this number, more than 80 per cent are fibers of chrysotile less than 5 microns long. Patients in the general population who have pleural plaques have about the same total number of fibers, but their lungs contain about a 50-fold increase in long thin amphibole fibers of commercial origin. Patients who have asbestosis and most patients who have mesothelioma have 100 to 200 X 10(6) fibers/g dry lung; the grade of asbestosis appears to be related to total fiber content. Occasional patients may develop mesotheliomas with much smaller fiber burdens. Both benign and malignant pleural diseases appear to be closely related to the presence of long thin amphibole fibers. Analysis of pulmonary fiber burden suggest that asbestos-related disease is not merely a matter of total numbers of fibers present, but that factors such as fiber type and size are equally important.

In plain English

This 1982 single-author review covered the relatively few published studies that had counted and identified asbestos fibers and asbestos bodies in human lung tissue, including the author's own. It also described electron microscope methods for identifying fibers. In one reviewed study of 20 autopsy patients without occupational exposure, the average was 1.29 million uncoated fibers per gram of dried lung, 80 per cent chrysotile. In 29 autopsy patients with pleural plaques, total fibers were about the same, but commercial amphiboles were increased almost 50-fold. One reviewed study compared 99 mesothelioma patients with 99 matched controls and saw no difference in chrysotile. Among the 76 men, 26 patients and 8 controls had more than 1 million amosite fibers per gram of dry lung. In workers with high amphibole exposure, fiber counts rose with the grade of asbestosis. Asbestos bodies measured only a small part of total fibers. The author concluded that fiber type, and possibly length and shape, mattered more than total fiber numbers. The author cautioned that methods were not standardized and that most conclusions rested on one or two articles and small patient numbers.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: review of published studies of asbestos fiber and asbestos body counts in lung tissue, including the author's own studies
• Who was studied: Lung tissue from groups in the reviewed studies: general-population autopsy patients without occupational exposure, autopsy patients with pleural plaques, workers with high-level exposure and asbestosis, Quebec chrysotile mining industry workers, and patients with mesothelioma or lung cancer and their controls
• Exposure: Asbestos fibers found in lung: chrysotile; the commercial amphiboles amosite and crocidolite; and the non-commercial amphiboles anthophyllite, tremolite and actinolite
• Main results:
  • In 20 autopsy patients without occupational asbestos exposure (Churg and Warnock), the average was 1.29 x 10^6 uncoated fibers per gram of dried lung, of which 80 per cent were chrysotile
  • In 29 autopsy patients with pleural plaques, the average number of asbestos bodies was 17,000 per gram. Total fibers were about the same as in controls, but commercial amphiboles were increased almost 50-fold
  • About half of the pleural plaque patients had shipyard or construction work. These patients had about 20 times the number of commercial amphiboles found in the control group
  • In the reviewed McDonald et al. study of 99 mesothelioma patients and 99 matched controls, no difference in chrysotile was seen between patients and controls. In Table 4, 26 of the 76 male mesothelioma patients had more than 1 x 10^6 amosite fibers per gram of dry lung, compared with eight male controls
  • In the reviewed Whitwell et al. study, which counted only fibers visible by light microscopy, 87 of 88 mesothelioma patients with known asbestos exposure had more than 20 x 10^3 fibers per gram of dry lung
  • In workers with high-level amphibole exposure (Ashcroft and Heppleston), fibers visible by phase microscopy rose from about 2.4 x 10^6 per gram of dry lung without asbestosis, to about 19 x 10^6 with grade 1 asbestosis, to 200 x 10^6 with grade 2 asbestosis
  • The author's group analyzed the cores of almost 600 asbestos bodies from people who were not asbestos workers. Of these, 98 per cent had an amphibole core and 2 per cent a chrysotile core
  • Counts of uncoated fibers indicated that asbestos bodies measure only a very small part of the total asbestos burden, except with very high exposure
• The authors' conclusion: The author concluded that everyone carries a background asbestos burden of about 1,000,000 fibers per gram. The author also concluded that the type of fiber, and possibly its length and aspect ratio, are more critical than the total number of fibers, and that long, high-aspect-ratio commercial amphiboles appear the most dangerous. The author judged asbestos bodies to be markers of exposure, not indicators of disease.
• Limitations the authors state:
  • Techniques and ways of expressing results differ from laboratory to laboratory and are not standardized
  • For most categories, the conclusions rest on one or two articles and relatively small numbers of patients
  • Some table values were converted between units and from distributions to means. Assuming that each case fell at the midpoint of a range may give spuriously high figures
  • Wet-to-dry weight conversions used a factor of 10, which may not be correct for data from other laboratories
  • Fibers may be unevenly distributed in the lung, so small biopsy samples may not be reliable indicators of lung asbestos load

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Chrysotile, Crocidolite.

Medical terms in this study, explained in our Lexicon: Fiber Counting, Asbestos Exposure, Asbestos Bodies, Chrysotile, Pleural Plaques, Amphibole Group, Mesothelioma, Fiber Burden.

Related studies

• Fiber burden and patterns of asbestos-related disease in chrysotile miners and millers — A. Churg, J.L. Wright, et al. (1993)
• Fiber burden and patterns of asbestos-related disease in workers with heavy mixed amosite and chrysotile exposure — A. Churg, S. Vedal (1994)
• Patterns of histopathological change determined by the point counting method and its application for the hazard assessment of respirable dust — A. Ogami, Y. Morimoto, et al. (2004)
• Pulmonary mineral fibers after occupational and environmental exposure to asbestos in the Russian chrysotile industry — A. Tossavainen, E. Kovalevsky, et al. (2000)
• Solubility of asbestos and man-made mineral fibers in vitro and in vivo: its significance in lung disease — A. Morgan, A. Holmes (1986)
• Standardized methods for preparation and bi-variate length & diameter counting/sizing of aerosol and tissue digestion fiber samples — D.M. Bernstein, P. Kunzendorf (2018)

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