National Safety Editorial April 2018

BATTERY OF HEARING TESTS, MINIMISING REFERRALS



Hearing is one of our most precious senses and when damaged can affect job performance, health, as well as personal and occupational productivity. Hearing damage from noise is fully preventable when the right precautions are taken. Despite all that is known about noise and its effects on health, NIHL remains one of the most commonly reported occupational diseases. Our hearing should be evaluated holistically to ensure optimal total hearing care. Workers working in high noise areas or who are exposed to noise at or above 85dB(A) must be submitted to medical surveillance for hearing screening.

Effective case history taking has long been identified as a core discipline in treating people that seek health care. Collecting an inaccurate or incomplete history can affect initial treatment and subsequent decisions for intervention. Prior to audiometric testing, the worker must undergo an otoscopic examination to ascertain the presence of any abnormalities which could adversely influence the accuracy of the test results. A screening hearing test should then be performed if the outer ear does not present with abnormalities e.g. impacted wax, foreign bodies, or infections. To ensure reliable and accurate test results any “abnormal” condition should be referred and/or treated before testing commences. When abnormal hearing thresholds are identified after the screening test, the client is referred for further diagnostic tests to determine the actual cause of the hearing loss.

A full diagnostic hearing evaluation is performed for the specific purpose of a specialist evaluation of an individual’s hearing status, employing immittance measurements, otoacoustic emissions, pure tone audiometry (air conduction, bone conduction, masking), as well as speech audiometry. However, complimentary tests that could be included within the screening test battery are Immittance measurements and Otoacoustic measurements.

Immittance measurements are conducted to evaluate the middle ear system objectively. It consists of tympanometry and acoustic reflex testing. With tympanometry, a tone is delivered to the ear while pressure is changed within a sealed ear canal. This test measures the volume, pressure and compliance (motility) of the middle ear system to determine if there are any abnormalities. Tympanometry has numerous advantages which include: it is fast and easy to perform, requires no response from the patient, is an objective measurement and is portable. This test is not a stand-alone test but is used as a cross-check gainst the audiogram to develop a more complete picture of an individual’s hearing. It also has an important role in differentiating a sensorineural hearing loss from a conductive hearing loss.

Otoacoustic emission (OAE) testing should also be performed as part of the test battery. This test examines the outer hair cell functioning of the inner ear. With this test a stimulus is presented into the ear canal and the response of the outer hair cells to the stimulus are recorded via a probe. When recording otoacoustic emissions the patient’s middle ear functioning should be normal, therefore immittance measurement should be conducted before OAE testing. Performing OAE testing has several advantages: it can be incorporated as a screening and diagnostic application, does not require behavioural cooperation, is ear and frequency specific, is portable and is highly sensitive to outer hair cell damage. OAEs are in addition to the diagnostic process and not a replacement to previously trusted methods; this is because OAEs are susceptible to the effects of noise, affected by middle ear status, may be absent or abnormal with a normal audiogram, are not detectable with hearing loss >40dB and, therefore, they are ultimately not a test of hearing.

It is evident that when hearing screening is performed a variety of tests are required. These screening tests can be done cost effectively and reliably on site reducing the number of incorrect referrals and thereby saving considerable costs.

For more information please contact H.A.S.S. Industrial (Pty) Ltd – Your Partner in Hearing Conservation. We are an official distributor of Industrial Hearing Screening equipment and the manufacturer of Noise-Ban custom-made hearing protection devices.

View Our Range here. For more visit www.hearingprotection.co.za or contact us on (012) 403-8740 or E-mail: communications@hass.co.za

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