The chest radiograph is problematic, however, when trying to diagnose minimal or mild disease. Is a radiographic finding of a mild increase in interstitial lung markings (ie, a mild increase in small, irregular opacities [ILO grade, 1/0 and 1/1]) adequate by itself to diagnose asbestosis? Although chest radiographic findings usually are abnormal in patients with asbestosis, about 10 to 15% of the time they may be relatively normal,26,43–
which yields a sensitivity of 85 to 90%. Furthermore, many factors other than asbestos exposure can lead to a mildly abnormal chest radiographic finding, affecting its specificity. These factors include, for example, radiographic technique, aging, obesity, smoking, presence of COPD, and exposure to various other fibrogenic and nonfibrogenic dusts.44–
In addition, the radiologic diagnosis of mildly abnormal has a rather large interobserver variation. For example, in one study45
in which 23 “B-readers” certified by the National Institute of Occupational Safety and Health evaluated 105,029 chest radiographs for the assessment of asbestosis among naval personnel, there was a 20-fold difference in the prevalence of positives findings (ILO grade, ≥ 1/0) between the extreme readers, and the average prevalence was 2.4%. Welch et al46
reviewed the interobserver variation in chest radiograph interpretation of pneumoconiosis, finding that among the same 119 chest radiographs that were read by six qualified readers, the number that were read as being positive for asbestosis (ILO grade, ≥ 1/0) varied from 24 to 91%. This problem, of course, significantly affects sensitivity and specificity. If, in fact, 91% of the group actually had asbestosis, the individual who found it in only 24% would exhibit a very poor sensitivity of, at best, 24 of 91 patients (26%). Conversely, if 24% were the correct figure, the individual who diagnosed it in 91% of the people would exhibit very poor specificity of, at best, 9 of 76 patients (12%).