The National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group

Our plain-English summary of The National Sheet Metal Worker Asbestos Disease Screening Program: radiologic findings. National Sheet Metal Examination Group, by L.S. Welch, D. Michaels, S.R. Zoloth (American Journal of Industrial Medicine, 1994).

The study

• Authors: L.S. Welch, D. Michaels, S.R. Zoloth
• Journal: American Journal of Industrial Medicine
• Published: 1994;25(5):635-48
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

This report presents data gathered from a series of asbestos disease screening examinations of 9,605 United States sheet metal workers who were first employed in the trade at least 20 years before the examination. The overall prevalence of asbestos-related radiographic changes was 31.1%: 18.8% had pleural abnormalities alone, 6.6% had parenchymal abnormalities (International Labour Office (ILO) score of 1/0 or higher) alone, and 5.7% had both. Among those with 40 years or more since entering the trade, 41.5% had radiographic signs of asbestos-related disease, 24.2% pleural alone, 7.7% parenchymal alone, and 9.6% both pleural and parenchymal abnormalities. After controlling for several surrogates for asbestos exposure level, cigarette smoking was found to increase risk of parenchymal, and more modestly, pleural abnormalities. Each pack-year was associated with a 1% increased prevalence odds ratios for parenchymal abnormalities (ILO category 1 compared to category 0), and 0.4% increased prevalence odds ratios for pleural abnormalities. A history of shipyard employment also produced significantly increased prevalence odds ratios for each radiographic category. More that 90% of chest radiographs were classified by A or B readers; after adjustment for other risk factors, A readers were more likely to report parenchymal abnormalities of category 1, but not more likely to report category 2 or pleural abnormalities, than B readers.

In plain English

This cross-sectional screening study examined chest X-rays of 9,605 U.S. male sheet metal workers who had entered the trade at least 20 years earlier. Sheet metal workers do not ordinarily use asbestos directly. Overall, 31.1% had X-ray changes consistent with asbestos exposure: 18.8% had pleural abnormalities alone, 6.6% had parenchymal (lung tissue) abnormalities alone, and 5.7% had both. Among the 2,552 workers with 40 or more years since entering the trade, the figure was 41.5%. After adjustment for age, years since entering the trade and years worked, each pack-year of smoking was associated with about a 1% higher prevalence odds ratio for parenchymal abnormalities, and a smaller rise for pleural abnormalities. Reported shipyard work was associated with more than double the odds of parenchymal abnormalities and about 30% higher odds of pleural abnormalities. A readers reported more category 1 parenchymal findings than B readers. The authors noted that selective participation and differences between readers may have affected overall rates. They concluded that this group, once considered lightly exposed, showed a substantial prevalence of abnormalities.

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 analysis of a standardized asbestos disease screening program: questionnaire, physical examination, spirometry and chest radiograph read using the ILO classification, with logistic regression giving prevalence odds ratios
• Who was studied: 9,605 U.S. male sheet metal workers first employed in the trade at least 20 years before examination. They were screened at U.S. clinics starting in 1986. In the first round, 12,454 of 26,329 eligible workers were examined, a participation rate of 47%. Workers with incomplete data, workers seen at one clinic with a faulty X-ray machine, and female workers were excluded. Mean age was 57.2 years.
• Exposure: Asbestos exposure during sheet metal work. The work does not itself use asbestos; exposure came from working near insulation workers and sprayed asbestos fireproofing, and from retrofitting. No fiber types are named. The analysis used surrogates for exposure: years since entering the trade, years worked, and shipyard, railroad, military or pre-trade asbestos exposure. Cigarette pack-years were also studied.
• Main results:
  • All 9,605 workers: 2,984 (31.1%) had asbestos-related radiographic changes. Of these, 1,806 (18.8%) had pleural abnormalities alone, 634 (6.6%) had parenchymal abnormalities alone (ILO 1/0 or higher), and 544 (5.7%) had both.
  • The 2,552 workers with 40 or more years since entering the trade: 41.5% had abnormalities, made up of 24.2% pleural alone, 7.7% parenchymal alone and 9.6% both.
  • Parenchymal changes were mostly in ILO major category 1. Less than 1% of all workers were classified 2/1 or higher.
  • Smoking and parenchymal abnormalities: each pack-year raised the prevalence odds ratio by about 1%. For ILO 1/0 to 1/2 the odds ratio was 1.011 (95% CI 1.009 to 1.014); for 2/1 or higher it was 1.012 (95% CI 1.004 to 1.021). By smoking status, there was a significant trend from never-smokers to ex-smokers to current smokers (p = .003).
  • Smoking and pleural abnormalities: the per-pack-year prevalence odds ratio was 1.004 (95% CI 1.002 to 1.006). The trend across never-, ex- and current smokers was not statistically significant.
  • Shipyard employment history, after adjustment, was associated with higher prevalence odds ratios. For parenchymal ILO 1/0 to 1/2 the odds ratio was 2.28 (95% CI 1.84 to 2.83); for 2/1 or higher it was 2.42 (95% CI 1.23 to 4.71); for pleural abnormalities it was 1.33 (95% CI 1.11 to 1.59).
  • Railroad employment, military asbestos exposure and asbestos exposure before entering the trade were not associated with increased risk of parenchymal changes.
  • Reader type: A readers reported more ILO category 1 parenchymal abnormalities than B readers (odds ratio 1.83, 95% CI 1.57 to 2.14). There was no difference between reader groups for category 2. Readers who were neither A nor B readers reported fewer abnormalities. Reported parenchymal prevalence was 11.2% among B readers, 17.5% among A readers and 4.9% among other readers.
• The authors' conclusion: The authors concluded that the survey showed a substantial prevalence of radiographic abnormalities in a group that did not use asbestos directly and had been considered to have light exposure. They also concluded that the findings confirm the value of large-scale screening of workers with past asbestos exposure.
• Limitations the authors state:
  • Overall rates may have been affected by selective participation and by variability between X-ray readers.
  • Each film was read by only one reader, which limits comparison between centers.
  • There was no independent check of the questionnaire data or of X-ray technique and quality.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Odds Ratio, Chest X-Ray.

Related studies

• Asbestos-related disease among sheet-metal workers. Preliminary results of the National Sheet Metal Worker Asbestos Disease Screening Program — L.S. Welch, D. Michaels, et al. (1991)
• Asbestos disease in sheet metal workers: II. Radiologic signs of asbestosis among active workers — D. Michaels, S. Zoloth, et al. (1987)
• Mortality among sheet metal workers participating in a respiratory screening program — L. Welch, J. Dement, et al. (2015)
• Asbestos-related disease among sheet metal workers 1986-2004: radiographic changes over time — L.S. Welch, E. Haile (2009)
• Comparative quantitative evaluation of pleural fibrosis and its effects on pulmonary function in two large asbestos-exposed occupational groups--insulators and sheet metal workers — R. Lilis, A. Miller, et al. (1992)
• Change in prevalence of asbestos-related disease among sheet metal workers 1986 to 2004 — L.S. Welch, E. Haile, et al. (2007)

Browse more research in American Journal of Industrial Medicine, or return to medical research.