Extended high-frequency audiometry for early detection of noise-induced hearing loss

Abstract

Noise-induced hearing loss (NIHL) is a common occupational health challenge that often develops gradually and remains unnoticed until significant damage has occurred. Conventional audiometry, which assesses pure tone thresholds up to 8 000 Hz, may not always detect early cochlear changes caused by noise exposure. Extended high-frequency audiometry (EHFA), which measures thresholds beyond 8 000 Hz, has been proposed as being more effective in identifying hearing loss not yet visible on conventional audiometry. This study investigated the effect of different categories of occupational noise exposure on EHFA thresholds to assess its potential as an early indicator of occupational noise-induced hearing loss (ONIHL). The study aimed to determine the effects that varying noise levels may have on EHFA and whether these effects are more pronounced in workers exposed to higher noise levels. A retrospective, quantitative study design was used to analyse audiometric data from 180 participants divided into three occupational noise exposure groups based on A-weighted decibels: category 1 (<85 dBA), category 2 (85–104 dBA), and category 3 (≥105 dBA). A hearing conservation programme (HCP) was implemented in the study setting, and hearing protection devices (HPDs) were mandatory within designated noise zones. Participants in categories 2 and 3 were subject to the administrative controls specified in the HCP and were provided with HPDs by their employer to meet these requirements. To focus on early auditory changes, stratified random sampling included participants with clinically normal hearing thresholds at conventional audiometric frequencies (500 – 4 000 Hz, thresholds <25 dB HL). All participants underwent both conventional pure tone audiometry (500 – 8 000 Hz) and EHFA (9 000 – 20 000 Hz). Audiometric thresholds were analysed using multivariate analysis of variance (MANOVA) and logistic regression to assess the effects of varying noise exposure levels, age, and years of service on EHFA thresholds. Conventional audiometry thresholds ranged from -10 dB to 50 dB HL, while EHFA thresholds ranged from -10 dB to 100 dB HL. Overall threshold patterns were comparable across noise exposure categories, with no statistically significant differences observed in either conventional or EHFA thresholds based on noise exposure level (p = 0.511) or years of service (p = 0.745). However, age emerged as a significant factor affecting hearing thresholds, particularly at 6 000 Hz, 8 000 Hz, and across all extended high-frequency (EHF) thresholds (p < 0.05). This study found limited evidence to support the use of EHFA as a tool for detecting early NIHL in the occupational setting. Instead, a strong influence of age on EHF thresholds was found, which underscores the need to account for age-related changes when interpreting EHFA data. The absence of significant EHF threshold deterioration across noise exposure categories may suggest that the HCP is effective in mitigating new cases of ONIHL. However, it is essential to note that the audiometer's limited maximum output intensity at EHFs may also contribute to the lack of significant findings. Future research using longitudinal designs should explore the applicability of EHFA in diverse occupational contexts and whether EHFA may be helpful in assessing the effectiveness of HCPs.