A routine for the control of the performance of microscopists evaluating airborne asbestos fibre samples on membrane filters by phase contrast microscopy

Our plain-English summary of A routine for the control of the performance of microscopists evaluating airborne asbestos fibre samples on membrane filters by phase contrast microscopy, by J.R. Hoyes, R. Clayton (The Annals of Occupational Hygiene, 1980).

The study

• Authors: J.R. Hoyes, R. Clayton
• Journal: The Annals of Occupational Hygiene
• Published: 1980;23(4):381-401
• Cited by: 5 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

By the use of slide circulations within a laboratory with slides of sufficient density to keep the Poisson error low and re-instruction as required, the relative performance of a team of membrane filter counters has been controlled such that 88 % of results obtained for performance checking purposes were within ±30% of the laboratory mean over the period November 1977-March 1980. Analysis of the results obtained indicates that the inherent standard deviation of the results from a counter is typically 16%. The slides circulated were prepared by the acetone-triacetin mounting method. There is no conclusive evidence from the data presented that during the period mentioned the slides have deteriorated.

PubMed has no abstract for this study. This is the authors' abstract, copied from the article.

In plain English

This paper described the quality-control routine a company laboratory, TBA Industrial Products Ltd in Rochdale, used to keep its microscopists consistent when counting chrysotile asbestos fibres on membrane filter slides. It was not a health study. From November 1977 to March 1980, three 'standard' chrysotile slides were circulated each month. Each counter's result was compared with the laboratory mean, and counters were re-instructed when needed. The aim was to keep each counter within plus or minus 30% of that mean. Of 620 results, 88.4% were within those limits. In August 1979, with a stable team of five counters, the authors calculated an inherent counter standard deviation of 15.7%. On 15 triacetin slides, the spread between counters (individual, overall and inherent standard deviations) was not significantly different from that in the laboratory's main checking data. A fall in performance during 1979 was attributed to less care by counters and team changes, not slide deterioration. The authors concluded that control within plus or minus 30% was achieved for 88% of results, and that permanent reference slides are needed for better absolute control.

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: Laboratory quality-control study: an internal slide-circulation routine for checking the performance of microscopists counting asbestos fibres by phase contrast microscopy
• Who was studied: The team of slide counters at the TBA Industrial Products Ltd laboratory (never more than six at a time; counters labelled A to I), November 1977 to March 1980; a stable team of five counters in August 1979
• Exposure: Not a health exposure. Slides were chrysotile fibre samples, mounted by the acetone-triacetin method, from a plant mainly producing asbestos textiles. Some triacetin-mounted slides were also counted.
• Main results:
  • Of the 620 performance-check results from November 1977 to March 1980, 88.4% were within plus or minus 30% of the laboratory mean; the overall standard deviation was 19.1%
  • For the August 1979 data from a stable team of five counters, 92.1% of results were within plus or minus 30% by inspection
  • Analysis of variance on the August 1979 data gave an inherent counter standard deviation of 15.7%, higher than the 10% predicted by Busch et al. from mostly low-density slides
  • Five of the eight individual counters' distributions of differences from the laboratory mean were not significantly different from Normal distributions; the overall distribution was slightly non-Normal
  • For 15 triacetin slides counted by five counters, the individual, overall (17.7%) and inherent (16.0%) standard deviations of counters' differences from the laboratory mean were not significantly different from the equivalent figures for the data in Tables 1 and 2
  • A double blind trial in April 1980 using standard slide 1 gave results very similar to previous months, which the authors took as showing that repeated circulation did not lead counters to return a constant remembered result
  • A fall in counting performance during 1979 was concluded to result from less care by counters and a change in team members, not from deterioration of the slides; afterwards performance returned to the 1978 level
• The authors' conclusion: The authors concluded that control within plus or minus 30% of the laboratory mean was achieved for 88% of results. They found the inherent counter standard deviation was typically 16%. They judged repeated circulation of standard slides, and acetone-triacetin slides when triacetin is used routinely, to be valid. They stated that permanent reference slides are needed for better absolute control.
• Limitations the authors state:
  • Results were expressed relative to the laboratory mean, so they were not independent: a large change in one counter could falsely suggest that others had changed. With a small team this inter-dependence can be large.
  • The overall standard deviations and distributions were influenced by changes in counters over the period and by their experience
  • It was not known whether the acetone-triacetin standard slides would be permanent in fibre counting terms, and the data could give no conclusive absolute evidence on slide deterioration

Topics

Medical terms in this study, explained in our Lexicon: phase contrast microscopy (PCM), Triacetin.

Related studies

• The influence of external aerodymanic factors on the measurement of the airborne concentration of asbestos fibres by the membrane filter method — A.M. Johnston, A.D. Jones, et al. (1982)
• A comparison of historic asbestos measurements using a thermal precipitator with the membrane filter-phase contrast microscopy method — G. Burdett (1998)
• Performance of membrane filters used for TEM analysis of asbestos — J.S. Webber, A.G. Czuhanich, et al. (2007)
• Sample preparation method for visualization of nanoparticulate captured on mixed cellulose ester filter media by enhanced darkfield microscopy and hyperspectral imaging — N.M. Neu-Baker, A.C. Eastlake, et al. (2019)
• A technical comparison of evaluating asbestos concentration by phase-contrast microscopy (PCM), scanning electron microscopy (SEM), and analytical transmission electron microscopy (ATEM) as illustrated from data generated from a case report — R.F. Dodson, S.P. Hammar, et al. (2008)
• Comments on Dodson et al., A technical comparison of evaluating asbestos concentration by phase contrast microscopy (PCM), scanning electron microscopy (SEM), and analytical transmission electron microscopy (ATEM) as illustrated from data generated from a case report — V.L. Roggli, T.A. Sporn, et al. (2008)

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