J. Soc. Occup. Med. (1990) 40, 117

Letter to the Editor

Classification of Audiometric Results

Sir,

A number of classification systems have been proposedfor assessment of hearing loss from audiograms, whichis of particular importance in the context of assessmentof disability, for example as a result of occupational noiseexposure. Among the systems currently used are thatproposed by the British Association of Otolaryngologists1,which expresses hearing loss as a percentage disability,and the simple numerical system put forward in theHealth and Safety Executive Discussion DocumentAudiometry in Industry1. This document never progressedbeyond the discussion stage, although the classificationsystem has been widely discussed in occupational healthcircles since it was published. It classifies audiograms intofive groups as below, the low frequencies being 0.5, 1 and2 kHz, and the high frequencies being 3, 4 and 6 kHz.

Category I. The first category applies if the sum of thehearing levels for either high or low frequencies showsan increase of 30 dB or more when compared with theimmediately preceding audiogram, or 45 dB when theinterval since the preceding examination exceeds 3 years.

Category 2. This applies when the difference of the sumsof hearing levels between the two ears exceeds 45 dB forthe low frequencies or 60 dB for the high frequencies.

Category 3. The third category is the 'warning level'.

Category 4. This is the 'referral level'.

Each of these categories is calculated from a table ofhearing levels for different age ranges, thereby taking intoaccount the effects of presbyacusis.

Category 5. This applies to the rest, i.e. normal audio-grams.

However, the use of a single numerical classificationsystem does not allow for situations where the resultmight fall into more than one category, as for examplethe individual showing a unilateral 'referral level' hearingloss, which has progressed since the last audiogram. Itis suggested that three sets of parameters need to berecorded, i.e. whether or not

(a) a previous audiogram has been performed, and, ifso, whether there has been any change in the successiveaudiogram;

(b) there is any significant difference in the hearingthresholds of the two ears;

(c) there is any significant hearing loss, i.e. category 3or 4 in the proposed HSE classification.

Use of the following three digit system enables simpleclassification of audiometric results, using the samecriteria as in the HSE Discussion Document, without theloss of information associated with the use of a singledigit system.

First Digit0 No change from previous audiogram, using HSE

criteria1 Significant change from previous audiogram, using

HSE criteria6 No previous audiogram

Second Digit0 No difference between the two ears, using the HSE

criteria2 Significant difference between the two ears, using HSE

criteria

Third Digit3 HSE 'Referral level'4 HSE 'Warning level'5 No significant loss

Hence, for example, an individual who has no previousaudiogram, and shows no significant hearing deficit willbe coded as 605. An individual with a previous audio-gram, significantly changed, with a different threshold ineach ear, and falling into the referral category will becoded 123. The system is presented as a simple extensionof the HSE proposal, and our experience has shown thatcomputerized audiometry systems can be programmedto undertake the classification without difficulty. It hasthe advantage of being simpler than most other systemscurrently in use, without the loss of information that isinevitable with a single digit system.

R. A. COOKEChief Medical Officer,GKN pic,Redditch,Worcestershire, UK

REFERENCES1. Method for Assessment of Hearing Disability. Br Assoc Otolaryngol

and Br Soc Audiology, 1983.1 Health & Safety Executive Discussion Document, Awllometry in

Industry, 1978.

'i~, 1990 Butterworth-Heinemunn for SOM0301-0023/90/0301 17-01

The British Occupational Hygiene Society

Seventh International Symposiumon Inhaled Particles

Edinburgh, 16-20 September

The Seventh International Symposium on Inhaled Particles will be held at the new Edinburgh ConferenceCentre on the Heriot Watt University Campus in Edinburgh. The Proceedings of the Symposium will againbe refereed, edited and published.

The Symposium will be concerned primarily with advances in understanding the basic mechanisms ofdeposition and clearance of dusts, their biological reactions and epidemiological studies. Topics will include:

Factors affecting the measurement of inhaled fraction;New models of deposition;Biological reactions of dusts in the lung;Synergistic effects of gases and dusts;Exposure - response studies of fibres, silica and other dusts;The role of different minerals in mixed dust pneumoconiosis;Dust or chemical exposure in relation to occupational asthma; andEffects of radon exposure and indoor air quality.

For further information please contact: Dr A. Robertson, Organising Secretary, Institute of Occupational Medicine, RoxburghPlace, Edinburgh, EH8 9SU, UK.

Occupational Health PracticeThird Edition

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