Quantifying What Better-Ear PTA4 Does Not Capture: High-Frequency and Asymmetric Classification Discordance in Two Independent Adult Population Samples from Germany and the United States.

Background/Objectives: The four-frequency better-ear pure-tone average (PTA4; 0.5-4 kHz) is the dominant population definition of hearing impairment but underweights frequencies above 4 kHz and ignores interaural asymmetry. We quantified, in two independent adult samples, the proportion of PTA4-normal adults with elevated high-frequency or asymmetric profiles and whether this has a self-report correlate. Methods: Cross-sectional secondary analysis of two public datasets: the German HÖRSTAT/Aalen sample (2008-2012; N = 3105) and pooled US NHANES (2011-March 2020; N = 10,575; adults ≥ 20 years). The primary outcome, PTA4-discordant high-frequency loss, was defined a priori as better-ear PTA4 ≤ 25 dB HL with a better-ear 6-8 kHz mean (PTA68) > 25 dB HL, reported as the conditional proportion among PTA4-normal adults. Secondary outcomes were interaural asymmetry ≥ 15 dB and self-rated hearing trouble (NHANES AUQ054 ≥ 3). Results: Among PTA4-normal adults, 34.3% (95% CI 32.5-36.2) of the German sample and a survey-weighted 28.2% (25.9-30.5) of the NHANES sample had PTA68 > 25 dB HL. Prevalence rose with age (≈three-fold odds per decade; two-fold for male sex; all p < 0.001). Of those with PTA68 asymmetry ≥ 15 dB, 75-85% remained PTA4-normal, although the more stringent unilateral-like pattern was rare (1.5-1.7%). Self-reported trouble was elevated in PTA4-discordant mild (OR 2.56) and strong (OR 3.50) groups (OR 1.43 per 10 dB PTA68). Conclusions: Although disagreement between the two classifications is arithmetically expected, since they cover different frequencies, its magnitude is substantial and reproducible: roughly a quarter to a third of PTA4-normal adults (28-34%) carry an elevated PTA68, with a graded self-report correlate consistent with early high-frequency presbyacusis, and the same age structure emerges in two samples measured with different equipment and procedures. Because the 25 dB HL criterion is not age-referenced, an increasing share of the discordance at older ages represents expected presbyacusis rather than pathology, so the older-age figures should be read as counts above a fixed public-health threshold. Reporting a high-frequency companion metric (PTA68 or PTA346) alongside PTA4 would make this information visible without displacing the existing system.