Auditory Differences in Occupationally Noise-Exposed Workers With Normal Conventional Audiograms: A Multi-Measure Surveillance Approach

Young adults with normal conventional audiograms may nonetheless show early noise-related auditory differences that routine surveillance misses. We evaluated a clinically feasible test battery using 280 occupationally noise-exposed workers and 100 age-matched low-noise controls (20-40 years; ≤20 dB HL at 0.5-8 kHz). Measures included conventional and extended high-frequency (EHF; 9-16 kHz) audiometry, distortion-product otoacoustic emissions (DPOAEs; 0.5-10 kHz), ipsilateral acoustic reflex thresholds (ARTs; 0.5, 1, and 2 kHz; 226-Hz probe tone), click-evoked auditory brainstem responses (ABR; wave I, wave V, and V/I ratio at 50 and 90 dBnHL), and Mandarin Bamford-Kowal-Bench speech-in-noise testing (SiN). Noise-exposed participants showed elevated ARTs at all elicitor frequencies, with the largest elevation at 2 kHz, as well as poorer EHF thresholds and lower DPOAE levels. In contrast, click-evoked ABR metrics did not differ between groups. After controlling for conventional-frequency pure-tone average (PTA ₄ ; 0.5, 1, 2, and 4 kHz) and extended high-frequency pure-tone average (PTA _EHF ; 9–16 kHz), lower DPOAE amplitudes were associated with higher ARTs. ARTs were not significantly associated with SiN performance, quantified as the signal-to-noise ratio (SNR) required for 50% correct recognition (SNR-50), cumulative noise exposure, or ABR measures. The noise-exposed group showed higher SNR-50 values, indicating poorer speech-in-noise performance. Within the noise-exposed group, SNR-50 was associated with PTA ₄ and cumulative noise exposure, whereas its association with PTA _EHF was weaker and did not remain significant after correction for multiple comparisons. Together, these findings suggest that cochlear-status measures, conventional ARTs, and functional SiN performance provide complementary information beyond the conventional audiogram in occupational hearing surveillance.