Early prognosis of noise-induced hearing loss

Objective Occupationally acquired noise-induced hearing loss (NIHL) is the most prevalent occupational disease in Austria and among the most common in many other countries. Because of the wide variation in hearing loss after equivalent exposures it has long been assumed that some individuals are more vulnerable to occupational NIHL than others. Earlier attempts to define predictors of NIHL before starting occupational noise exposure have largely failed. We present results of a prospective study evaluating the potential of temporary threshold shift (TTS) after a test exposure to predict NIHL. Methods Between 1982 and 1989, overall 311 apprentices were included into a prospective study during their initial health screening visit. At this occasion, a standardised noise exposure was applied (20 min, 200-500 Hz, 100 dBA) and the TTS at 4 kHz was determined during at least 10 min after exposure. Hearing loss was monitored at follow-up visits every 3-5 years. Follow-up was 13 years on average. Results Permanent threshold shift was predicted by duration of noise exposure, frequency of wearing noise protectors and especially by the initial TTS at 4 kHz. Using 14 dB TTS as a cut-off had 82% sensitivity and 53% specificity to predict 20 dB or higher levels of NIHL. Conclusions The TTS model can be successfully applied as a method to detect individuals at greater risk of occupational NIHL. It is recommended to routinely include such a procedure into initial workers' examinations for suitability to work under occupational noise conditions and for counselling on the use of hearing protectors.