Discrepancies of asbestos body and fiber content between formalin-fixed and corresponding paraffin embedded lung tissue

Our plain-English summary of Discrepancies of asbestos body and fiber content between formalin-fixed and corresponding paraffin embedded lung tissue, by B.K. Kuhn, F. Barresi, H. Dressel, et al (Inhalation Toxicology, 2021).

The study

• Authors: B.K. Kuhn, F. Barresi, H. Dressel, B. Vrugt
• Journal: Inhalation Toxicology
• Published: 2021;33(1):18-24
• Cited by: 2 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Background: Formalin-fixed lung tissue and paraffin blocks containing peripheral lung tissue obtained from subjects with an occupational asbestos exposure are both regarded to be suitable to determine asbestos load. Because sample preparation of paraffin blocks requires a more intense treatment than formalin-fixed tissue, we tested whether asbestos analysis of formalin-fixed lung tissue and paraffin blocks obtained from the same patients deliver comparable results.

Materials And Methods: We determined numbers of asbestos bodies (AB) and amphibole asbestos fibers (AF) in formalin-fixed lung tissue and corresponding paraffin blocks from 36 patients. For AB counts, samples were digested in sodium hypochlorite. For AF analysis, tissue was freeze-dried and then ashed. Results were reported as numbers of AB and AF per gram dry lung tissue.

Results: Both AB counts as well as AF counts were lower in paraffin blocks than formalin-fixed lung tissue. Compared to formalin-fixed tissue, the limit of detection was higher for paraffin blocks, rendering more results from paraffin blocks not interpretable than from formalin-fixed tissue (8 samples versus 1 for AB and 15 samples versus 4 for AF).

Discussion And Conclusion: Asbestos analysis of paraffin blocks may lead to underestimation of asbestos exposure. This should be considered when assessing occupational asbestos exposure through lung dust analysis in medico-legal evaluation.

In plain English

This laboratory study from Zurich, Switzerland, which the authors called a quality control project, tested whether lung tissue kept in formalin and lung tissue embedded in paraffin blocks from the same patients give the same asbestos counts. The tissue came from 36 patients (5 with asbestosis, 6 mesotheliomas, 18 lung carcinoma and 7 non-asbestos related lung diseases), giving 46 paired samples. The authors counted asbestos bodies and amphibole asbestos fibers. Paraffin blocks more often fell below the limit of detection. For asbestos bodies, only the paraffin block was below it in 8 pairs, only the formalin-fixed tissue in 1, and both in 4. For fibers, the figures were 15, 4 and 11. Among pairs that could be compared, counts tended to be lower in paraffin blocks, a statistically significant difference. Under the Helsinki criteria cutoffs, the two materials put 18% of the 33 compared pairs into different categories for asbestos bodies, and 56% of 16 evaluated pairs for fibers. The authors concluded that using paraffin blocks increases the risk of false-negative results, with possible medico-legal implications. They said larger studies are needed to confirm their observations.

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 method-comparison study (described by the authors as a quality control project) comparing paired samples of formalin-fixed lung tissue and paraffin blocks from the same patients
• Who was studied: 36 patients (5 with asbestosis, 6 mesotheliomas, 18 lung carcinoma, 7 non-asbestos related lung diseases). Their formalin-fixed lung tissue and paraffin blocks were retrieved from the archives of the Swiss laboratory for particle analysis in tissues (silag), Zurich. There were 46 tissue pairs in total because 6 patients had samples from multiple sites. Dates are not given.
• Exposure: Not a study of exposure levels as such. Lung asbestos burden was measured as asbestos bodies (light microscopy) and amphibole asbestos fibers (transmission electron microscopy with chemical identification by EDX). Only amphibole fibers were reported because the Helsinki criteria are based on amphiboles.
• Main results:
  • Asbestos bodies: 33 of 46 pairs were above the limit of detection in both materials. In 8 pairs the formalin-fixed count was above the limit and the paraffin block count below it. The opposite occurred in 1 pair, and both were below the limit in 4 pairs.
  • Asbestos bodies: each paraffin block count was compared with the spread of the four single counts in formalin-fixed tissue. It was within that spread in 58% of cases, lower in 33% and higher in 9%.
  • Asbestos bodies: among the analyzed pairs (the 33 with both counts above the limit of detection), 82% fell in the same Helsinki criteria category and 18% were classified differently between formalin-fixed tissue and paraffin blocks
  • Asbestos bodies: the paired differences between formalin-fixed tissue and paraffin blocks differed significantly from zero (Wilcoxon signed-rank test, p = 0.038; p = 0.017 after log transformation)
  • Asbestos bodies: the Bland-Altman analysis of log-transformed data gave a mean paired difference of 0.2
  • Amphibole fibers: only 16 of 46 pairs could be evaluated. In 15 pairs only the paraffin block was below the limit of detection, in 4 only the formalin-fixed tissue was, and in 11 both were.
  • Amphibole fibers: of the 16 evaluated pairs, 70% of paraffin block samples showed considerably lower counts. Allowing for 50% variability, paraffin blocks were lower in 10 cases (62%), overlapped in 4 (25%) and were higher in 2 (12%).
  • Amphibole fibers: under the Helsinki criteria, 7 of 16 pairs (44%) fell in the same category and 56% were misclassified. In 2 cases the paraffin block result was higher; in the other 7 it was lower.
  • Amphibole fibers: the paired differences differed significantly from zero (Wilcoxon signed-rank test, p = 0.008; p = 0.003 after log transformation). The Bland-Altman analysis of log-transformed data gave a mean paired difference of 0.7.
• The authors' conclusion: The authors concluded that asbestos body counts, and especially amphibole fiber counts, are often lower in paraffin blocks than in formalin-fixed tissue. They said physicians should be aware that measuring asbestos burden in paraffin blocks increases the risk of false-negative results, which may have medico-legal implications.
• Limitations the authors state:
  • The authors stated that larger studies are needed to confirm their observations
  • The authors noted that the smaller asbestos body discrepancy could be argued to reflect uneven distribution of asbestos in lung tissue
  • The authors noted that paraffin block samples were of poorer quality, which hampered reliable counting
  • The authors noted that the small paraffin block samples may not be representative, because variation in fiber counts within them cannot be determined

Topics

Medical terms in this study, explained in our Lexicon: Asbestos Body Formation, Paraffin Block, Asbestos Exposure, Asbestos Bodies, Amphibole Asbestos.

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