Crackles in the early detection of asbestosis

Our plain-English summary of Crackles in the early detection of asbestosis, by R.L. Murphy, E.A. Gaensler, S.K. Holford, et al (The American Review of Respiratory Disease, 1984).

The study

• Authors: R.L. Murphy, E.A. Gaensler, S.K. Holford, E.A. Del Bono, G. Epler
• Journal: The American Review of Respiratory Disease
• Published: 1984;129(3):375-9
• Cited by: 33 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. 000559).

Abstract

We studied 386 workers exposed to asbestos to assess the value of chest auscultation by a trained technician in detecting asbestosis as defined by previously reported clinical, physiologic, and roentgenologic criteria. The presence and degree of crackles were assessed at preselected basilar lung sites by a technician whose performance was validated by comparison with computer-generated time-expanded waveforms of tape recordings of lung sounds. Asbestosis was present in only 2.8% of the total population, but it was present in 8.6% of those with over 25 yr or more of employment. The technician correctly identified all the workers in whom the diagnosis was most certain, that is, those with all criteria positive. The overall true positive rate was 55%. The majority (94.8%) of those with no abnormal criteria were correctly classified. Auscultation by an objectively validated technician can be a useful noninvasive method for screening industrial populations exposed to asbestos.

In plain English

The authors studied 386 asbestos-exposed workers from paper and insulation manufacturing and a shipyard. They tested whether a trained technician listening for lower-lung crackles could detect asbestosis. Asbestosis meant at least 3 of 4 criteria: irregular X-ray opacities at profusion 1/2 or more, single-breath diffusing capacity below 80% predicted, vital capacity below 80% predicted, and crackles at two or more lower-lung sites. Eleven workers (2.8%) met this definition, as did 8.6% of the 93 workers with over 25 years of employment. The technician identified all 4 workers meeting all four criteria but missed 5 of the 7 meeting three; the overall true positive rate was 55%. The technician correctly classified 94.8% of workers with no abnormal criteria. In 20 of 22 recordings, the technician's on-site classification (score 3 or more versus less) agreed with two observers' readings of computer-generated waveforms. Crackle scores were associated with smoking. The authors suggested low scores may reflect smoking, while high scores were associated with asbestosis. The authors concluded that listening to the chest by a properly trained, objectively validated technician can be a useful screening method.

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 study of asbestos-exposed workers, comparing a validated technician's assessment of lung crackles with other criteria for asbestosis
• Who was studied: 386 asbestos-exposed workers from paper and insulation manufacturing and a shipyard; 93 had over 25 years of employment. The article does not state where or when the workers were surveyed.
• Exposure: Occupational asbestos exposure in the manufacture of paper and insulation materials and in a shipyard. Fiber types and doses are not given. Exposure was described by years of exposure or employment.
• Main results:
  • Asbestosis, defined as 3 or 4 of 4 criteria, was found in 2.8% of all 386 workers (11 workers: Table 1 lists 7 with 3 criteria and 4 with 4 criteria) and in 8.6% of the 93 workers with over 25 years of employment. It did not occur in workers with less than 11 years of exposure. The criteria were irregular X-ray opacities at a profusion of 1/2 or more, single-breath diffusing capacity below 80% predicted, vital capacity below 80% predicted, and crackles at 2 or more basilar sites.
  • The technician correctly identified all 4 workers who met all 4 criteria.
  • The overall true positive rate was 55%. The technician missed 5 of the 7 workers with 3 of 4 positive criteria (false negatives).
  • The technician correctly classified 94.8% of workers with no abnormal criteria.
  • When physicians' crackle findings were left out of the asbestosis criteria, the technician identified 80% of workers with all 3 remaining criteria.
  • The technician's on-site classification (weighted crackle score of 3 or more versus less than 3) agreed in 20 of 22 recordings (90.9%, Kappa 0.80) with waveform interpretations (positive or negative for crackles). Those interpretations were made by 2 observers, who read the computer-generated time-expanded waveforms while listening to the recorded sounds. Separately, the technician agreed with a computer classifier on fine versus coarse crackles in 84.4% of cases (Kappa 0.68).
  • The weighted crackle score was associated with pack-years of smoking among the 366 workers with smoking data (chi-square 19.35, p less than 0.005). From a regression analysis, the authors suggested that scores of 1 or 2 may reflect smoking, while a score of 3 or more is associated with asbestosis.
  • Crackle prevalence did not correlate significantly with symptoms of chronic bronchitis, obstruction on lung function testing, or X-ray evidence of emphysema.
  • Workers with high crackle scores but no other criteria had a longer average exposure than the whole group: 19.6 versus 13.8 years.
• The authors' conclusion: The authors concluded that listening to the chest by a properly trained and objectively validated technician can be a useful method for screening asbestos-exposed industrial populations, and that further studies of sensitivity and specificity are warranted.
• Limitations the authors state:
  • The method makes errors, including false negatives. The breathing method used may have caused some of the false negatives.
  • It is difficult to separate crackles caused by the industrial exposure from those caused by cigarette smoking.
  • It is unknown whether the 'false positives' reflected milder asbestosis.
  • The criteria were designed for epidemiologic screening and do not replace clinical evaluation of suspected cases.
  • True positives may be underestimated.

Topics

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

Medical terms in this study, explained in our Lexicon: Basilar.

Related studies

• Lung crackle characteristics in patients with asbestosis, asbestos-related pleural disease and left ventricular failure using a time-expanded waveform analysis--a comparative study — N. al Jarad, S.W. Davies, et al. (1994)
• Diagnosis of asbestosis by a time expanded wave form analysis, auscultation and high resolution computed tomography: a comparative study — N. al Jarad, B. Strickland, et al. (1993)
• Asbestos in the sputum, crackles in the lungs, and radiologic changes in women exposed to asbestos — J.C. Davies, D. Kielkowski, et al. (2004)
• Computer-assisted diagnosis for early stage pleural mesothelioma: towards automated detection and quantitative assessment of pleural thickening from thoracic CT images — K. Chaisaowong, T. Aach, et al. (2007)
• Crackles (rales) in the interstitial pulmonary diseases — G.R. Epler, C.B. Carrington, et al. (1978)
• Computed tomography in the early detection of asbestosis — R. Bégin, G. Ostiguy, et al. (1993)

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