Validity of Estimating the ۳ kHz Audiometric Threshold by Averaging the Thresholds at ۲ and ۴ kHz in Cases of Noise-Induced Hearing Loss

Background: Hearing thresholds at ۳۰۰۰ Hz are generally not measured in routine clinical audiometry. However, for purposes other than clinical diagnosis, the threshold at ۳ kHz has many applications, in epidemiological studies in the field of occupational health and medicine, as well as in (medicolegal) quantification of physical impairment due to hearing loss, particularly noise-induced hearing loss (NIHL). The present study addressed the validity of estimating, in the case of NIHL, the ۳ kHz-audiometric thresholds by averaging the thresholds at ۲ and ۴ kHz. Methods: All ۲۰۰ investigated subjects (۴۰۰ ears) had a well-documented noise exposure, moderate to severe NIHL, and underwent, as they were claiming for compensation, a detailed medicolegal audiological investigation, including beside pure tone audiometry, electrophysiological objective frequency-specific threshold definition using cortical evoked response audiometry (CERA) and auditory steady-state response (ASSR). Results: The study results showed a good correlation between the ۲-۴ kHz interpolation and the actual ۳ kHz threshold; the error may be around ۲ dB on average. However, in individual cases, the results demonstrated that the error due to interpolation exceeds ۵ dB HL in about one-quarter of the cases. This error is predictable; the larger the ۲- ۴ KHz difference (which reflects the steepness of the left slope of the audiometric notch), the larger the error (on either side) made by interpolating. Conclusion: For epidemiological studies with large amounts of data, the interpolated threshold (average of ۲ and ۴ KHz) may be considered as a valid estimate of the true value of the ۳ KHz threshold. More caution is required in individual cases: the error due to interpolation exceeds ۵ dB HL in about one-quarter of the cases, but this error is predictable.  

Keywords:

Hearing Loss , Noise-induced , Audiometry , Evoked Response , Auditory Threshold