Is this STS work-related? ISO 1999 predictions as an adjunct to clinical judgment

Background: Physicians and audiologists are often asked to decide whether standard threshold shifts (STSs) are work-related; epidemiological data can inform these decisions. Methods: Predictions of ISO (2013) for both age-related and noise-induced threshold shifts, for the 2, 3, and 4kHz average used in calculating OSHA STSs, are presented, in tables, graphs, and an Excel spreadsheet calculator. Specifically, the ISO 1999 model estimates age-related thresholds based on age and sex; it estimates noise-induced threshold shifts based on noise level and duration. It specifies that to estimate the final hearing thresholds for a person of given percentile, age, sex, and noise exposure, the expected age-related threshold is to be added to the expected noise-induced threshold shift. Examples show how these data can predict the relative contributions of aging and occupational noise to an STS. Results: Early-career STSs, especially with high levels of noise exposure, are more likely to be primarily noise-induced. After the first decade of exposure, most STSs will be primarily age-related. Conclusion: Given a worker's age, sex, and occupational noise exposure history, ISO 1999 estimates of the expected contributions of aging and noise can supplement clinical judgment.