Asbestos-related pleural thickening: effect of threshold criteria on interpretation

Our plain-English summary of Asbestos-related pleural thickening: effect of threshold criteria on interpretation, by R. Greene, C. Boggis, H. Jantsch (Radiology, 1984).

The study

• Authors: R. Greene, C. Boggis, H. Jantsch
• Journal: Radiology
• Published: 1984;152(3):569-73
• Cited by: 27 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. 000539).

Abstract

Radiographic evidence of pleural thickening was evaluated in 1,216 shipyard workers (high-risk group) and 214 executives (low-risk group) and classified according to two threshold levels: low (any detectable thickening) and high (thickening less than or equal to 2 mm excluded). Results were markedly different, affecting the low-risk group more than the high-risk group. Changing from the high to the low threshold markedly increased pleural findings and scores as well as inter-reader correlation while reducing both differences between risk groups and detection of additional findings on supplementary oblique views. When data on prevalence and extent of pleural thickening were combined, differences between risk groups were maximized; however, when only prevalence was considered, such differences were minimized, particularly with a low threshold. These findings indicate that different or ambiguous threshold criteria produce divergent results in screening surveys for asbestos-related disease. The authors recommend that explicit minimal pleural threshold criteria be adopted.

In plain English

This study, from the radiology department of Massachusetts General Hospital, examined how the rule for what counts as pleural thickening on a chest X-ray changes survey results. Chest radiographs from 1,216 workers at six naval shipyards (the high-risk group; 48 were excluded) and 214 executives (the low-risk group) were scored under two thresholds. The low threshold counted any detectable thickening. The high threshold counted only 'definite' thickening and excluded thickening of 2 mm or less. Under the low threshold, overall prevalence did not differ significantly between the groups. Under the high threshold, there was a threefold difference between them. Switching from the high to the low threshold raised prevalence by a factor of 20 in the executives and by a factor of 4 in the shipyard workers. Pleural scores were higher in the shipyard workers under either threshold. In 50 roofers, adding oblique views raised prevalence fivefold (from 4% to 22%) under strict criteria and from 48% to 68% under broad criteria. The authors concluded that specific criteria and uniform methods are needed. They noted they lacked full job histories for the executives.

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: Cross-sectional comparison of chest radiographs from two groups with different occupational risk of asbestos exposure, each scored under two threshold criteria, with reader-consistency testing and a separate oblique-view substudy
• Who was studied: Low-risk group: 214 consecutive executives (195 men, 19 women) in a periodic health assessment program, 1971 to 1981. High-risk group: 1,216 workers (1,192 men, 24 women) from six naval shipyards in a radiographic asbestos surveillance program, 1979 to 1982. Forty-eight were excluded, leaving 1,147 men and 21 women aged 20 to 69. A separate set of radiographs from 50 roofers was used for the oblique-view assessment.
• Exposure: Occupational risk of asbestos exposure, defined by job group: naval shipyard workers (high-risk) versus executives (low-risk). The article names no fiber types and gives no exposure measurements.
• Main results:
  • With broad (low-threshold) criteria, the overall prevalence of pleural findings was not significantly different between the shipyard workers and the executives.
  • With strict (high-threshold) criteria, there was a threefold difference in prevalence between the two groups.
  • Pleural scores were higher in the high-risk (shipyard) group under either set of criteria (p less than 0.001). The difference was more marked with strict criteria.
  • Changing from the high to the low threshold increased prevalence by a factor of 20 in the low-risk group and by a factor of 4 in the high-risk group. This nearly cancelled the threefold difference between the groups.
  • Changing to the low threshold increased low-risk scores fourfold and high-risk scores by a factor of 1.5.
  • In the high-risk group, the prevalence of 'suspect' pleural thickening rose from 22.6% in the youngest decade to 66.7% in the oldest.
  • No pleural calcification was found in the low-risk group. In the high-risk group, 8 patients received the maximum score because of calcification.
  • Small irregular opaque areas in the lower lungs were seen in 2.6% of the high-risk group and in 2 people (1%) of the low-risk group.
  • In the 50 roofers, adding oblique views raised prevalence from 48% to 68% with broad criteria. With strict criteria it rose fivefold, from 4% to 22%. The article describes the broad-criteria increase as '1.7 times', but its own figures (48% to 68%) work out to about 1.4 times.
  • With broad criteria, agreement between two different readers was higher in both groups. Effects on the same reader's consistency were inconsistent.
• The authors' conclusion: The authors did not favor either threshold. They concluded that specific criteria and uniform methods are needed. They recommended recording all degrees of detectable thickening and applying stricter thresholds only after the readings are completed.
• Limitations the authors state:
  • The authors lacked comprehensive occupational histories for everyone in the low-risk group, so they could not rule out significant transient asbestos exposures in that group.
  • The source of 'suspect' pleural findings was unclear, as was the nature of the relatively high prevalence of findings in the low-risk group under broad criteria.
  • The authors stated that a lowered threshold is bound to increase the false-positive rate.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Asbestosis, Pleural plaques and thickening.

Medical terms in this study, explained in our Lexicon: Pleural Thickening.

Related studies

• Asbestos-related pleural diseases: dimensional criteria are not appropriate to differentiate diffuse pleural thickening from pleural plaques — J. Ameille, M. Matrat, et al. (2004)
• Cardiorespiratory responses to incremental exercise in patients with asbestos-related pleural thickening and normal or slightly abnormal lung function — A. Miller, A. Bhuptani, et al. (1993)
• Asbestos-related diffuse pleural thickening — N. Fujimoto, K. Kato, et al. (2014)
• Bilateral pleural thickening: a manifestation of asbestos dust exposure — E.N. Sargent, J. Gordonson, et al. (1978)
• Diffusing capacity and forced vital capacity in 5,003 asbestos-exposed workers: relationships to interstitial fibrosis (ILO profusion score) and pleural thickening — A. Miller, R. Warshaw, et al. (2013)
• Development, radiological zone patterns, and importance of diffuse pleural thickening in relation to occupational exposure to asbestos — H. Bohlig, A. Calavrezos (1987)

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