Experienced pulmonary and occupational medicine specialists took the medical histories and performed the physical examinations of all patients. Medical history comprises information on the present illness, past medical and surgical history, tobacco use history, family history, personal or social history, and comprehensive occupational history. The detailed occupational history documented the patients’ present and past employment history and identified types of dust exposures at their workplaces. The occupational group was referred to as the job presumed to be the cause of pneumoconiosis by the occupational physicians of the clinic. We used the recorded smoking history to calculate tobacco pack years by multiplying the average number of cigarette packs per day by the total number of smoking years.
Spirometry was performed using the Zan 100 flow-sensitive spirometry device (ZAN Messgerate GmbH, Oberthulba, Germany). The spirometer was calibrated daily, with measurements of temperature and humidity used for calibration. The spirometry results were analyzed based on the acceptability and reproducibility criteria presented in the ATS/European Respiratory Society statement updating the standardization of spirometry. The patients’ spirometry measurements were evaluated based on the percentage of the reference values.
Chest X-rays (CXRs) were taken with a digital X-Ray system. CXRs were evaluated by two readers separately and independently according to the International Labour Organization’s (ILO) International Classification of Radiographs of Pneumoconioses, and the results were obtained in consensus. Small opacities are described by profusion, shape (rounded or irregular), and size. Small opacity profusion is classified into four categories (0, 1, 2, 3), each divided into three subcategories (0/- to 3/+). ILO profusion scores of 1/0 and above are considered pneumoconiosis. Progressive massive fibrosis (PMF) is defined as a large opacity exceeding 1 cm in diameter assigned to one of three categories according to the ILO International Classification of Radiographs of Pneumoconioses.