Hearing Thresholds of Otologically Healthy 18-year-olds

Objective: To determine mean hearing thresholds for 18-year-old, otologically healthy subjects. Study design: Prospective historical cohort study. Methods: As part of a follow-up study of a birth cohort, followed from age 2 to 18 years, meticulous otological examination including history-taking, otoscopy, and audiometry were available. At age 18, both air-conduction thresholds (0.25 kHz to 8 kHz and 8 kHz to 16 kHz) and bone-conduction thresholds (0.5 kHz to 4 kHz) were measured. Subjects of this cohort were defined as otologically healthy if they had not experienced substantial otitis media in childhood. Results: On both ends of the frequency range of air-conduction testing, measured thresholds deviated statistically significantly from the ISO 389 reference zero. The air-conduction thresholds were comparable to data presented in the literature. Furthermore, a misfit with the ISO 389 reference was found at 2 and 3 kHz for bone-conduction testing. Only the mean boneconduction thresholds at 0.5 kHz and 4 kHz were not significantly different from the ISO 389 reference zero. To explain the deviations at high frequencies, noise exposure was considered but thought unlikely. Conclusions: This study cohort seems to be the best representative sample so far of otologically healthy subjects due to the longitudinal study of their otological status. Mean hearing thresholds at age 18 are different from the ISO 389 reference zero, suggesting once more the need to revise this ISO norm.