Guidelines for quantification of noise-induced hearing loss in a medicolegal context.

OBJECTIVES: Guidelines published in 2000 by the authors are widely used by medical and legal professionals in the UK for diagnosis of noise-induced hearing loss in a medicolegal context. However, they cannot be used for quantification of the noise-induced hearing loss, which is required in most cases. This requirement is addressed. DESIGN: A method is developed here to quantify noise-induced hearing loss, thereby overcoming this shortcoming. SETTING: Assessment of noise-induced hearing loss in medicolegal cases. PARTICIPANTS: A consecutive series of 124 cases of noise-induced hearing loss is used for evaluation. MAIN OUTCOME MEASURE: Magnitude of noise-induced hearing loss based on hearing threshold levels averaged over the frequencies 1, 2 and 3 kHz. RESULTS: The rationale of the method, practical application and three worked examples are developed. A simpler short-cut method is developed and shown to be equivalent to the full method in most cases. CONCLUSIONS: The method offers a practical approach to quantification of noise-induced hearing loss.

Asymmetric sensorineural hearing thresholds in the non-noise-exposed UK population: a retrospective analysis.

OBJECTIVES: To estimate the distribution of inter-aural sensorineural hearing threshold level differences in the non-noise-exposed adult population of the UK. SETTING: A two-stage population study carried out in 1979-1986, initially by postal questionnaire, followed up in a proportion of participants by clinical and audiological examination. PARTICIPANTS: Volunteers (n = 48 313) initially selected at random from the electoral registers of four cities, subsequently selected at random from questionnaire respondents stratified by answers to questions about hearing. MAIN OUTCOMES MEASURE: Inter-aural hearing threshold level differences measured audiometrically, as a function of age and gender. RESULTS: Tables of inter-aural threshold level differences provided as a resource with potential medicolegal, clinical and research applications. Based on the average of the frequencies 0.5, 1, 2 and 4 kHz, approximately 1% of the general UK population aged 18-80 years have an asymmetry of 15 dB or more. The prevalence is greater in older than in younger people. CONCLUSIONS: Inter-aural threshold differences greater than attributable to measurement error are not uncommon in the adult population, even after screening for conductive hearing loss and substantial noise exposure. They are typically of unknown origin.