Predictors of susceptibility to noise-induced hearing loss

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Published on 29 August 2014

A new study has shown that temporary threshold shift (TTS) can be used to detect individuals at greater risk of developing occupational noise-induced hearing loss (NIHL).

Individual susceptibility is known to play a very important role in the development of NIHL since hearing losses vary widely following identical levels of noise exposure. To date, results from studies that aimed to define predictors of NIHL before the start of occupational noise exposure have not been particularly conclusive.

Researchers from the Institute of Environmental Health at the Center for Public Health, Medical University Vienna (Austria) conducted a prospective study evaluating the potential of temporary threshold shift (TTS) to predict NIHL after test exposure. The study included 311 apprentices (fitters and welders) who were followed-up from the start of their professional activity for an average of 13 years. During their initial occupational health visit, they were exposed to standardized noise (20 min, 200-500 Hz, 100 dBA) and their TTS at 4 kHz was recorded for at least 10 minutes after exposure. Experimental exposure before start of work led to a wide range of TTS values, from 0 to 38 dB (average 16 dB). The participants were then monitored every three to five years for NIHL.

125 noise-exposed workers were evaluable at the final study assessment. Although age at onset of exposure was within a narrow range, duration of exposure in years covered a wide interval of about 2 to 22 years. The researchers carried out a regression analysis and found that for each increase of the experimental TTS of 10 dB, the predicted hearing loss increased by 2 to 3 dB, making TTS at 4 kHz a significant predictor of long-term NIHL.