Abstract

OBJECTIVES
Workers from a factory was selected to compare 8 standard threshold shift criteria with the Korean diagnostic criteria of noise-induced hearing loss for this cohort study.
METHODS
From 1990 to 1999, 491 workers at a manufacturing company with complete record of the hearing test covering the range of 0.5~6 kHz for 10 consecutive years were finally selected. Eight standard threshold shift criteria (15 dB once, NIOSH (1972), 10 dB average 3~4 kHz, OSHA STS, AAOHNS, 15 dB twice, 15 dB 1~4 kHz, OSHA STS twice) along with the Korean standard for diagnosing the noise-induced hearing loss (the average hearing threshold at 0.5, 1 and 2 kHz) were compared to calculate the degree of the threshold shift and the minimum time required to detect the change.
RESULTS
Those workers showing at least one positive shift in the 'once'criteria of NIOSH (1972) were 92.5%; the 'average'criteria of 10 dB average 3~4 kHz were 35.8%; 'twice'criteria of 15 dB twice were 44.4%. The duration from the baseline to the year showing the first positive shift was from 3.2 +/- 3.1 years (NIOSH, 1972) to 6.0 +/- 2.1 years (OSHA STS twice). The percentage of true positive shift ranging from 20.4% (AAO-HNS) to 69.8% (NIOSH, 1972). There were 10 (2%) which met the Korean diagnostic criteria of noise-induced hearing loss.
CONCLUSIONS
Currently the concept of hearing threshold shift in diagnosing the hearing loss was adopted in Korea thus in this study we determined the validity and the effect of the various hearing threshold shift criteria and showed that NIOSH (1972) criteria was the best of all. In the future, hearing data from various manufacturing workers should be compared to thoroughly evaluate the threshold shift criteria and to establish adequate standard for Korean workers.

• Keywords: Noise induced hearing loss;Threshold shift criteria;Cohort study