The Reliability and Relevance of Historical Occupational Audiograms: Testing Times

Audiometric testing of employees has played a central role in the management of risk of exposure of workers to excessive levels of noise in industry for many decades. Audiometry can detect early damage to hearing. Typically where used by prudent employers, the testing would have comprised self-recorded automated audiometry (such as Bekesy audiograms). The reliability and relevance of such historical occupational testing remains open to challenge by some medico-legal experts. This article examines the pros and cons of such historical testing in the context of assessing the merits of deafness claims where the results of such testing are at odds with more recent “diagnostic” audiograms.

Occupational Testing Versus Pure-Tone Audiometry

Two features are important: first, there is a general acceptance in “run of the mill” industrial deafness claims that audiometric changes as a result of noise exposure do not develop after cessation of exposure to noise. It should follow that reliable audiometric testing closer to the date of cessation of exposure is likely to be more representative of the effects of noise on an individual than later audiometry. Secondly, a diagnosis of noise-induced hearing loss can be considered against a set of guidelines, such as the Guidelines on the diagnosis of noise-induced hearing loss for medico-legal purposes by Coles, Lutman and Buffin, Clin. Otolaryngol. 2000, 25, 264-273, where, if diagnostic criteria are satisfied, it is likely to be accepted that an individual is suffering from noise-induced hearing loss if there has been sufficient exposure to noise. 

However, cases arise where there are several BSA-compliant audiograms which are diagnostic for the purposes of a medico-legal claim but where earlier occupational audiometry shows an absence of such diagnostic features. Often the claim is commenced on the basis of the recent audiograms and it is only at a later stage that earlier (non-diagnostic) occupational hearing tests come to light. Where it is considered that there is a good history of prolonged exposure to excessive levels of noise and there is a recent supportive audiogram, there is inevitably a natural reluctance on the part of a claimant to accept the reliability and relevance of earlier non-diagnostic occupational hearing tests. Is this justified?

The occupational audiograms should form part of disclosure of the claimant’s occupational health records. They are relevant to issues of limitation, causation and quantum. As such they will be admissible in evidence to the same extent as a claimant’s GP records. Any attempt to challenge the occupational hearing tests on the basis that they have not been proved is unlikely to be successful.

The principal arguments which are often raised to undermine the reliability of the occupational hearing tests are that: (1) BSA-compliant audiometry is considered the ‘gold standard’ for diagnostic purposes; (2) the occupational testing was for screening purposes; (3) no ENT consultant would use the screening test for diagnostic purposes; (4) studies which attempt to demonstrate the reliability of self-recorded automated audiometry (such as Bekesy audiograms) in comparison to manual audiometry are usually in ideal laboratory conditions and as such the studies are not relevant or applicable to real world tests in the context of industrial screening; and (5) if undertaken in less than ideal conditions, there would be factors which would impact accuracy on both sides such as testing conditions, equipment, tester and calibration.

On the other hand, the arguments deployed in favour of reliance on the earlier audiograms are that: (1) taking into account measurement error, the results often demonstrate consistency (either in one ear or both) particularly if over a series of independently conducted audiograms; (2) it is incorrect to infer that any changes within audiometric error make the audiogram less reliable (as by definition any changes within audiometric error are not significant); (3) there is an absence of any evidence that the occupational audiograms are inaccurate; (4) the earliest and best available audiogram provides no support for a diagnosis of noise-induced hearing loss; (5) systematic review has shown no statistically significant difference between automated threshold audiometry and manual audiometry (i.e. pure-tone audiometry); and (6) the technique of automated threshold audiometry is demonstrated to be scientifically valid.

In my opinion and based on recent experience, in an appropriate case, the latter arguments should prevail. Greater reliance can and should be placed on the earlier occupational hearing tests than on later BSA-compliant tests given their proximity to the noise exposure.

It can be anticipated that an attempt may be made to undermine the reliability of earlier occupational hearing tests in run of the mill industrial deafness claims by medico-legal experts adopting an unorthodox view that there has been progression of noise-induced hearing loss after cessation of noise exposure. They may argue that the diagnostic criteria only emerged after the occupational hearing tests were carried out. In my opinion this is a controversial issue and there is insufficient evidence to displace the orthodox view that damage from noise occurs at the time of exposure.

Conclusion

While each case will be determined on its own facts, a blanket argument that occupational hearing tests should be ignored when considering a diagnosis of noise-induced hearing loss is unlikely to succeed. The extensive use of occupational hearing tests in industry over many decades acted as an important part of the management of risk at the time. They continue to be useful many years later in establishing a baseline of a claimant’s hearing thresholds at the time of testing/exposure and when such exposure ceased. Indeed they may show that diagnostic criteria were present during the course of such noisy employment (which may be relevant to limitation issues). 

The existence of a system of occupational hearing tests may support a broader argument that this was an employer who had taken appropriate steps to manage the risks.

Of greater significance, in terms of causation, occupational hearing tests have an important role to play: generally they can be deemed reliable and relevant with the prospect of undermining the results of more recent BSA-compliant audiograms and providing a complete defence to a claim.