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On the Need for an “Industry-Wide Standard” Definition of an Audiometric Notch and the Lack of Specificity of the Audiometric Notch in the Diagnosis of Noise-Induced Hearing Loss

Morris, Robert J. MD, MPH

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Journal of Occupational and Environmental Medicine: May 2019 - Volume 61 - Issue 5 - p e226
doi: 10.1097/JOM.0000000000001550
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To the Editor:

The American College of Occupational and Environmental Medicine in September 2018 updated its Guidance Statement on Occupational Noise-Induced Hearing Loss.1 Previous versions had been published in 20032 and 2012.3 The typical appearance of the audiogram in noise-induced hearing loss (NIHL) is described in this way: “Its first sign is a ‘notching’ of the audiogram at the high frequencies of 3000, 4000, or 6000 Hz with recovery at 8000 Hz.”1 However, none of the Guidance Statements go beyond this general description and provide specific, objective criteria for detecting an audiometric notch.

Three points deserve to be made. The first point is that the lack of specific, objective criteria for detecting an audiometric notch has been shown to lead to substantial variation (from 35% to 65%) in the rate of detection of notches between experts who performed independent interpretations of a series of audiograms.4 The authors stated that, “The main problem here seems to be that there is no standard definition of an audiometric notch, so people tend to develop their own criteria.” To the extent that the presence of an audiometric notch is considered vital to the diagnosis of NIHL, the rate of diagnosis of that condition will vary widely between audiogram interpreters.

Secondly, the lack of specific, objective criteria for detection of an audiometric notch leads to intrainterpreter variation in the rate of detection of notches such that experts reading audiograms twice in a blinded manner agreed with themselves only 55% to 90% of the time.5 The authors concluded that “some experts were not internally consistent in their judgements about either the presence of a notch or of notch progression.” The authors called for further research that could lead to an “industry-wide standard” definition of an audiometric notch. To the best of my knowledge, such research has not been published, although various objective criteria for audiometric notches exist.6–11

The third point is the lack of specificity of the audiometric notch for the diagnosis of NIHL. Audiometric notches are commonly found in workers without significant occupational or non-occupational noise exposure.12–16 Nondahl et al13 stated that “notches can occur in the absence of a positive noise history” and found that individuals with a history of occupational noise exposure were only 8% to 36% more likely to have audiometric notches than those without such exposure. As stated by Lie et al,12 “The prevalence of Coles notch and notch index in the present study is approximately 60% in the exposed and 50% in the nonexposed group. This implies that the specificity of one notch as criterion for NIHL diagnosis is very low, as 5 of 6 notches may be unrelated to occupational noise exposure. The general rule that a hearing loss with a notch indicates an NIHL and the lack of a notch speaks against must be used with great caution.”

An “industry-wide standard” definition of an audiometric notch is urgently needed to help make the diagnosis of NIHL more consistent. Research into the possible causes of audiometric notches in individuals without noise exposure is also needed. Perhaps American College of Occupational and Environmental Medicine, in cooperation with other professional organizations involved in hearing conservation, will support the necessary research.


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