A comparison of fibre counting across three European national proficiency testing schemes

Our plain-English summary of A comparison of fibre counting across three European national proficiency testing schemes, by A.D. Jones, M.C. Arroyo, R. Grosjean, et al (The Annals of Occupational Hygiene, 2005).

The study

• Authors: A.D. Jones, M.C. Arroyo, R. Grosjean, B. Tylee, B.G. Miller, P. Brown
• Journal: The Annals of Occupational Hygiene
• Published: 2005;49(4):309-24
• Cited by: 3 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Proficiency testing (PT) schemes seek to improve and maintain consistency in asbestos fibre counting by circulating mounted samples to laboratories, which return counts for comparison with consensus reference values. This study compares the level of these consensus values in three (Spanish, Belgian and UK) national PT schemes. It also assesses the effect of the imminent change in the European standard rules for counting asbestos fibres, to the new rules from the World Health Organisation (WHO), which will include more fibres. Forty samples from the three schemes were circulated to six laboratories, two in each national scheme. The UK and Spanish laboratories counted using both the ERM and the WHO method. Belgian laboratories already use the WHO method, and they counted only by this method. Densities from counts in this sample exchange served as a common basis against which we compared the national reference values (R). This produced a geometric overall mean ratio of R to exchange mean density of 0.94 for the UK scheme, 1.01 for the Spanish and 0.97 for the Belgian scheme, and thus indicated remarkably similar levels. Nevertheless, non-trivial systematic inter-laboratory differences confirmed the need for regular PT and international inter-laboratory comparisons. Examination of previous data from the national PT schemes and from an international scheme (AFRICA) provided further comparisons for the same laboratories (either comparing the laboratory's data with R values or making direct comparisons between laboratories) that are consistent with those from this special exchange. The change in fibre counting rule (to include fibres apparently touching particles with diameter >3 microm) produced mean increases in reported densities that ranged among samples from 0 to 70% (highest individual estimate 170%); the effect was broadly similar for the three schemes. The laboratories gave mostly similar estimates of percentage increase; however, one laboratory occasionally produced high estimates indicating a possible need for training for using the new method.

In plain English

This laboratory study compared how three national proficiency testing schemes (UK RICE, Spanish PICC-FA and Belgian) count airborne asbestos fibres on microscope slides. In 2002, 40 reference slides from the schemes were counted by six laboratories, two per country. Each scheme assigns its slides a consensus reference value. UK and Spanish values were compared with exchange averages (geometric means) of European Reference Method counts, Belgian values with WHO-method counts. The ratios were 0.94 for the UK, 1.01 for Spain and 0.97 for Belgium. Individual laboratories differed from each other by non-trivial amounts. The study also measured the effect of WHO rules, which, unlike the European method, count fibres appearing to touch particles above a set diameter. The average ratio of WHO to European-method counts was 1.28 on Belgian slides, 1.20 on Spanish slides and 1.14 on UK slides. One laboratory occasionally gave much higher increases. The authors concluded that average counting levels were consistent across the three schemes, but that regular inter-laboratory comparisons are still needed. They noted that only a small subset of slides was used.

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: inter-laboratory sample exchange comparing fibre counts and reference values across three national proficiency testing schemes
• Who was studied: 40 reference slides (16 from the UK RICE scheme, 16 from the Spanish PICC-FA scheme, 8 from the Belgian scheme) counted in 2002 by six laboratories, two from each national scheme
• Exposure: Slides carried airborne asbestos dust from several sources. UK: eight removal or clearance samples with mostly amphibole fibres, and eight chrysotile samples from the asbestos textile industry. Belgium: eight samples understood to come from clearance, enclosure and maintenance work. Spain: sixteen laboratory-generated asbestos cement dust samples. Fibres were counted by the European Reference Method (ERM) and/or the WHO method. The WHO method includes fibres appearing to touch particles above a set diameter, which the ERM excludes.
• Main results:
  • UK and Spanish reference values were compared with ERM counts from the exchange. Belgian reference values, which are based on WHO counts, were compared with WHO counts.
  • The ratios of national reference values to the geometric mean densities from the exchange ranged from 0.94 (UK) to 1.01 (Spanish), a difference in average levels of about 5%.
  • For the Belgian slides, the national reference value was 0.967 times the geometric mean of WHO counts from the four UK and Spanish laboratories (shown as 0.97 in Table 2).
  • The UK scheme's reference values were, on average, slightly lower than those of the Belgian and Spanish schemes.
  • There were non-trivial differences in counting level between the six laboratories. For WHO counts on Belgian slides, laboratory mean ratios to the reference value ranged from 0.86 to 1.44.
  • The origin of the slides did not appear to have much effect on the differences between laboratories.
  • Mean ratios of WHO to ERM density were 1.28 for Belgian samples, 1.20 for Spanish PICC-FA samples and 1.14 for UK RICE samples (order per Table 5). Mean increases across samples ranged from 0 to 70%, with a highest individual estimate of 170%.
  • Spanish lab 2 produced a higher share of the high WHO-to-ERM ratios (mean 1.29 over all samples in Table 5).
  • Laboratories' counts in the exchange were generally consistent with their levels in previous years of their own national schemes.
• The authors' conclusion: The authors concluded that average counting levels are currently consistent among these three European national schemes. They also concluded that the differences between laboratories confirm the need for regular inter-laboratory comparisons and continued international monitoring.
• Limitations the authors state:
  • Only a limited number of samples was used from each scheme, for example 16 out of a stock of 900 in the RICE scheme.
  • The study ran over a few months in 2002 with a small subset of slides, so ongoing linkage between the schemes is needed to confirm the findings.
  • The UK and Spanish laboratories' normal level of WHO counting can only be known once they use the WHO method routinely.
  • Using the exchange counts as a common basis carries uncertainty from inherent counting variation and from systematic differences between laboratories.

Related studies

• A proposal for harmonising laboratory performance assessment criteria in national asbestos fibre counting schemes — M.C. Arroyo, J.M. Rojo (2001)
• Proposal to adapt the WASP programme to fibre counting tests — M. Grzebyk, E. Kauffer, et al. (2006)
• Producing samples for the organization of proficiency tests. Study of the homogeneity of replicas produced from two atmosphere generation systems — L. Freville, J.C. Moulut, et al. (2010)
• Continued participation in an asbestos fiber-counting proficiency test with relocatable grid slides — M. Harper, J.E. Slaven, et al. (2009)
• A comparison of fibre counting stopping rules in the application of the membrane filter method — N.P. Crawford, W.M. Maclaren, et al. (1987)
• Development of the KOSHA Proficiency Testing Scheme on Asbestos Analysis in Korea — J. Kwon, K. Jang, et al. (2017)

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