Audiometry update: Sound advice?

Back in 1980, the author of this article published a detailed paper describing the problems that would be experienced with the Health and Safety Executive (HSE) five-category audiogram analysis scheme which was then in force. This evidence was considered by the HSE, which moved swiftly to rectify the highlighted deficits by producing a revised scheme – a quarter of a century later.


Although published late in 2005, the new scheme was generally taken to be effective from April 2006, when the new UK Noise at Work Regulations came into force. We operate under that new scheme today, and its implications are only just becoming apparent.


The article itself deals with the management of the warning and referral categories resulting from utilisation of the new HSE audiogram analysis scheme. Details of the mechanics of the scheme itself can be obtained for free by e-mailing the author.


Old vs new


So what was wrong with the old HSE scheme?


Our original 1980 study applied the old HSE scheme to 9,115 audiograms measured in 29 industries on 37 different noisy sites. Alarmingly, it showed that under the scheme, only 46% of employees in noisy industries would be classified as normal. Some 23% would be deemed to have hearing bad enough for them to be referred to an authority such as their GP or company doctor for further attention, while an additional 30% would need warning letters about the state of their hearing.


All of this was caused by the fact that under the old scheme, an employee only had to exceed the average hearing loss for their age group by a small amount to be placed into one of the abnormal categories.


This national pattern was repeated for most of the companies that we visited in the 25-year interregnum that passed before the new HSE scheme commenced in 2006. The old scheme made the management of employees after an audiometric survey very difficult, due to the large numbers being referred for further medical attention. So is the new HSE scheme any better?


To find out, we ran a project in 2007 which took 1,207 audiograms measured using our mobile audiometric service in 12 noisy factories from 12 industries, and analysed them firstly according to the old HSE scheme, and then secondly by following the new 2005-06 HSE scheme.


The results are given in figure 1, and show a good correlation with the 1980 study, in that under the old HSE scheme, only 43% of the population would be considered normal, while 19% would be referred, and a further 38% would be warned about the state of their hearing.



The situation changes greatly, however, when the same population is analysed using the new HSE scheme. As shown in figure 2, the referral percentage drops from 19% to 7%, and those needing to be warned about their hearing drops from 38% to 13%. This means that the percentage classified as normal rises from only 43% under the old HSE scheme, to 80% under the new HSE scheme.


At first glance, this decrease in the number of individuals referred seems to be an improvement – but as always there are consequences, which are presently causing the occupational health (OH) practitioner a few problems.


Consequences


Firstly, those who created the new HSE scheme would never claim to have caused “…the deaf to hear again and the dead to be raised” (Luke 7:22). All that has happened is that the new scheme is more lax, meaning some employees who were placed in one of the abnormal categories when tested under the old scheme, would now be pulled out of that category and placed into a less worrying one under the new scheme.


However, the OH practitioner needs to be diplomatic when explaining this to a person affected by this process, as an astute employee could ask some penetrating questions, such as: “Which classification system is correct – the old or the new?”


The relaxation of the audiometric scheme, however, can also present other difficulties when deciding upon patient management after an audiometric test classified under the new scheme.


Take the audiogram shown in figure 3. Even though the employee is 60, it is reasonable to feel that his hearing loss is such that he might soon be considering the use of a hearing aid. You would therefore expect that Mr Dodds should fall into an abnormal category – and yet the classification under the new HSE scheme is Category 1, normal for age; not even category 2 – warning.



In order to assess whether this Category 1 classification is reasonable, further calculations have been performed on Dodds’ audiogram, the results of which are shown by the shaded lines on the audiogram, and the dotted line. The calculation method chosen was that specified in the International Organisation for Standardisation’s ISO 1999 standard, with a comparative population database A, as detailed in ISO 7029. Of all the methods available, it is thought that this is the one most acceptable to the courts.


There is insufficient space in this article to explain how this evaluation method works, but we do deal with it on the Industrial Audiometry courses that we present. In summary, however, we all lose our hearing at a different rate as we age, due to individual susceptibility to the ageing process. The calculations referenced in the preceding paragraph compare Dodds’ hearing with that of a non-noise exposed population of individuals of the same age. The results are shown in figure 3. The crosses show the left ear acuity, and the circles the right ear acuity. The top of the grey zone represents the hearing loss to be expected in the 25% of men of Dodds’ age who are the most resistant to hearing loss caused by ageing. The white line through the middle of the grey zone represents the median hearing loss to be expected. The lower bound of the grey zone shows the hearing loss to be expected as a result of ageing in the 25% of most deafness-prone men of Mr Dodds’ age. Finally, the dotted line shows the hearing loss to be expected in the 5% of individuals of Dodds’ age who are most susceptible to the effects of ageing.


Although the new HSE scheme classifies Dodds as being normal for his age, Figure 3 indicates that at times, his hearing is close to, or worse than, that of the poorest 5% of individuals his age. Throughout the rest of the range, it is around the level of the worst 10% of individuals his age. Hardly a case for telling him that he has “acceptable hearing levels” as specified by the HSE for individuals in category 1.


And it is not just in the case of employees of Dodds’ age that we see this problem – it occurs throughout the whole age range. So what can we do?


Precautionary measures


1 When using the new HSE audiogram analysis scheme, OH practitioners performing audiometry need a greater degree of training than before on what constitutes a reasonable audiogram so that they can manage the employee’s results effectively.


2 OH staff need to make sure that they have returned their audiometers to specialist companies to make sure that they have had new analysis chips fitted, so that the instruments analyse audiograms following the new HSE scheme. Unfortunately, audiometers are still in use today analysing audiograms using the old HSE scheme. The old scheme and the new scheme produce a diagnostic printout that is deceptively similar in appearance, but radically different in meaning. The old HSE scheme used categories 1, 2, 3, 4 and 5. The new HSE scheme uses categories 1, 2, 3, 4 and U. Spot the difference.


3 Some OH practitioners believe that the old and new schemes are similar, stating that the new scheme is “just a renaming exercise on the categories”. This is not true – the new scheme is far more lax, different in its calculation procedure, produces fewer referrals, is different for the two sexes, and the apparently identical numerical categories actually have different meanings.


4 OH departments need to make a note in their files of the date on which their audiometers were converted to the new HSE scheme. Already it is becoming difficult to look at old audiometric records and instantly tell whether the data was analysed under the new scheme or the old. Obviously, manual recalculation of the audiogram thresholds would show the vintage of the analysis scheme, but who has time for that?


5 Audiometricians should use the Bekesy zig-zag technique for measuring audiometric thresholds, not the manual method or the Hughson Westlake method (sometimes called the computer method) if they want to reduce the percentage of the tested employees that need to be referred for further medical attention. There is not space in this article to explain why, but contact the author by e-mail if you want to follow up this point.


6 And finally – make sure that you retest any employee before sending them off to the GP with their audiogram. You may be able to save both the employee’s time and that of their GP or company medical officer.


Dr Stephen Karmy is managing director of SJK Scientifics Ltd on the Science Park of Southampton University, and presents many of the Bilsom courses. Tel: 023 80 767954 E-mail: stephen.karmy@sjkscientifics.com


References




  • Karmy, SJ et al (1980) ‘Industrial Audiometry: The referral problem’ Disorders of Auditory Function III, editors Taylor and Markides. Academic Press London pp197-209


  • HSE (2005) Controlling Noise at work: Guidance on regulations, Document L108 ISBN 0-7176-6164-4. HSE books Sudbury.


  • Day, JM ( 2007) ‘Noise Induced Hearing Loss – has the introduction of the control at work regulations 2005 made a material difference to the number of people affected in the workplace?’ BSc. Audiology Dissertation. ISVR. University of Southampton.

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