High-Frequency Pseudo-Cohort Threshold Change and Severity-Dependent Sex Disparity in 4-kHz Audiometric Notching in Korean Adults

Objectives.: Using contemporary 2019-2023 Korea National Health and Nutrition Examination Survey (KNHANES) audiometry, this study estimated population-level pseudo-cohort hearing-threshold change and the prevalence and correlates of 4-kHz audiometric notching in Korean adults aged ≥40 years. Methods.: We included 12,576 adults aged ≥40 years with valid harmonized otolaryngologic/audiometry examination weights and sufficient audiometric data. Survey-weighted regression estimated pseudo-cohort hearing-threshold slopes within seven reconstructed five-year birth-cohort groups (1944-1978), after excluding the oldest reconstructed group affected by age top-coding at 80 years. A 4-kHz notch was defined when the 4-kHz threshold exceeded both the 2-kHz and 8-kHz thresholds by ≥ 10 dB in either ear; notch analyses were restricted to participants with classifiable person-level status. Survey-weighted multivariable regression identified notch- associated factors. Results.: High-frequency (4-8 kHz) pseudo-cohort slopes were approximately 1.7-9 times larger than low-frequency (0.5-1 kHz) slopes. In the youngest reconstructed birthcohort group (1974-1978, aged 41-49 years), high-frequency change was detectable (+0.97 dB/year) despite minimal low-frequency change (+0.11 dB/year). Among participants with classifiable notch status, the survey-weighted 4-kHz notch prevalence was 17.9%, corresponding to approximately 5.4 million adults. The male-to-female prevalence ratio increased from 3.0:1 at ≥10 dB to 4.5:1 at ≥15 dB and 7.3:1 at ≥20 dB, indicating severity-dependent sex disparity. In the primary model, male sex (OR 3.45), occupational noise exposure (OR 1.60), education level (OR 0.89 per level), and rural residence (OR 1.18) were associated with the notch. The apparent age-related decline in notch prevalence was consistent with presbycusis-related masking. Conclusion.: High-frequency threshold change was detectable in midlife and showed steeper population-level pseudo-cohort slopes than speech-frequency PTA. The 4-kHz notch was concentrated in midlife men, showed severity-dependent male predominance, and became less detectable with advancing age, consistent with presbycusis-related masking of notch geometry.