'B-readers' and asbestos medical surveillance.

"B-readers" certified in International Labor Office methodology interpret large numbers of randomly distributed asbestos medical surveillance roentgenograms of US Navy employees. Analysis of 23 participating observers, interpreting more than 105,000 radiographs, demonstrated a 300-fold prevalence range of perceived "definite" pulmonary parenchymal abnormalities. There was an evident geographic component to interpretation habits, with East and West Coast observers more likely to interpret films as abnormal than observers from the midcontinent. The most expert observers, a group who instruct the course leading to National Institute for Occupational Safety and Health certification in International Labor Office methodology, also perceived fewer abnormalities than other readers or coastal observers. Instructors still exhibited a sevenfold prevalence range of positive interpretation. Under usual surveillance conditions, the habits of B-readers appear to have a major impact upon the diagnosis of asbestosis from roentgenograms. Certification in B-reading should not be the only quality assurance for radiographic surveillance programs, medical decision-making, epidemiologic comparisons, nor related legal activities.