Chapter Outline

Occupational Screening Audiometry Chapter 8 Chapter Outline

Chapter Outline

Types of hearing tests	Types of audiograms
Specific audiogram criteria	Worker preparation
Factors influencing the validity of an audiogram	Malingering in audiometry

Educational Aims

After studying this chapter, you should be able to:

Explain the different tests used to assess hearing
Discuss the different types of audiograms performed in occupational health
Understand the criteria for each type of audiogram
Correctly identify the type of audiogram required after interpreting the history
Discuss the factors influencing the validity of audiometric testing
Identify and manage malingering in audiometry

Key Terms / Abbreviations


Abbreviation	Explanation
≤	These symbols mean equal to or less than
≥	This symbol means equal to or greater than
ABHL	Average Binaural Hearing Loss
AMER	Acoustic Middle Ear Reflex
CC	Compensation Commissioner
COIDA	Compensation of Occupational Injuries and Disease Act No. 130 of 1993 (including Instruction 171)
dB	Decibel
DMRE	Department of Mineral Resources and Energy
ENT	Ear Nose and Throat specialist
HCP	Hearing Conservation Program
HPD	Hearing Protective Device
HTL	Hearing Threshold Levels
Hz	Frequency
MHSA	Mine Health and Safety Act No. 29 of 1996
NIHL	Noise-Induced Hearing Loss
NRL	Noise Rating Level
OHNP	Occupational Health Nurse Practitioner (Nurse)
OHP	Occupational Health Practitioner (Nurse or Doctor)
OMP	Occupational Medicine Practitioner (Doctor)
OHS Act	Occupational Health and Safety Act No. 85 of 1993
PD	Permanent Disability
PLH	Percentage Loss of Hearing
PLHS	Percentage Loss of Hearing Shift
PTAC	Pure Tone Air Conduction
PTS	Permanent Threshold Shift
SANS	South African National Standards
SASOHN	South African Society of Occupational Health Nurse Practitioners
SASOM	South African Society of Occupational Medicine
STS	Standard Threshold Shift
TTS	Temporary Threshold Shift
Term	Definition
Accurate, Reliable, and Valid	In audiometry, this means correct in all details and exact (accurate). Consistently good in quality therefore able to be trusted. As the information is factually sound (reliable); and being legally binding or acceptable (valid). Therefore, meeting the required standards and criteria.
Amplitude	The loudness or intensity (volume) of the sound is determined by the amplitude (height) of the sound wave. Amplitude is measured in decibels (dB)²
Attitude	A settled way of thinking or feeling about something.
Audiometric Zero	Means the milestone baseline.
Baseline Audiogram	The baseline audiogram is the reference audiogram (1st audiogram ever performed) on a worker when exposed to noise equal to or above 85dB(A) for the first time. This the audiogram against which all future audiograms are compared to determine the extent to which an employee's hearing deteriorates if exposed to noise equal to or above 85dB(A) at work.
Bilateral	Involves both ears (Binaural).
Bone conduction Testing	In bone-conduction testing, instead of using an earphone, an electromechanical earphone is placed on the skull usually on the bony prominence behind the pinna. This allows for stimulation of the cochlea via mechanical vibration of the skull with almost no stimulation of the outer and middle ear (air conduction). Bone conduction thresholds should be equal to or better than air conduction thresholds in the same ear. Bone conduction thresholds are marked with an for the left side.
Compensation	The act of being paid for a disability. In worker's compensation, the degree of disability is important. It is reflected in percentages, then used to determine how much money will be paid as either a lump sum or once-off payment to the worker.
Compensation Commissioner	The Compensation Commissioner (CC) is appointed under section 2(1)(a) of the Compensation for Occupational Injuries and Diseases Act, 1993 (Act 130 of 1993); one of the responsibilities of the CC is to determine the validity of a claim, determine the degree of disability and payment of compensation to the claimant⁸.
Competent Person	(a) a person registered in terms of the Health Professions Act, 1974 (Act 56 of 1974), with the Health Professions Council of South Africa in any of the following three categories— (i) Otorhinolaryngologist (ear, nose, and throat specialist); (ii) speech therapist and audiologist; or (iii) occupational medicine practitioner; or(b) a person with a qualification in audiometric techniques obtained from an institution registered with the South African Qualification Authority or any of its structures in terms of the South African Qualifications Authority Act, 1995 (Act 58 of 1995), and registered with the South African Society for Occupational Health Nursing (SASOHN).¹¹
Descending Order	(of sound) becoming lower in pitch.
Conductive Hearing Loss	Conductive hearing loss (CHL) occurs when there is a problem transferring sound waves anywhere along the pathway through the outer ear, tympanic membrane (eardrum), or middle ear (ossicles).
Diagnostic audiometry	Measurement of hearing threshold levels and other parameters to determine the nature (for example, conductive, sensory, neural, or mixed) and degree of hearing impairment. It is performed by an audiologist registered with the Health Professions Council of South Africa.
Equivalent Continuous Rating Level	The equivalent continuous A-weighted sound pressure level during a specified time interval, plus a specified adjustment for impulsiveness of the sound, as contemplated in SABS 083.
Exaggerated Hearing Loss	Is hearing loss that does not exist or does not exist to the degree presented, regardless of psychological motivation, typified by inconsistencies and discrepancies but lacking medical explanation.
Exit Audiogram	An exit audiogram is performed at the termination of an employee’s service, contract or on the conclusion of exposure to noise equal to or greater than 85dB(A) in a workplace.
Frequency	Frequency is the speed of the vibration and this determines the pitch of the sound (highness and lowness of the sound). Frequency is measured in Hertz (Hz)²
Functional Hearing Loss	Nonorganic (functional) hearing loss is characterised by hearing loss without a detectable corresponding pathology in the auditory system.
Hearing Threshold Level Shift	A threshold shift is an increase in the hearing threshold for a particular sound frequency. It means that the hearing sensitivity decreases and that it becomes harder for the listener to detect soft sounds.
Hearing Threshold Levels	Hearing thresholds are defined as the lowest level of sound that can be heard 50% of the time.
Initial / Entry Audiogram	An entry audiogram is a single complete audiogram which is conducted on a new employee starting at a company or site for the first time who has been exposed to previous noise equal to or above 85dB(A) or who presents with an invalid baseline audiogram or is an employee is moved from one department to another and noise exposure increases.
Malingering	Malingering, or the falsification of hearing loss, is a frequent occurrence in many audiology clinics. This occurs particularly frequently when clinicians participate in the evaluation of individuals involved in medico-legal action such as worker's compensation cases.
Masking Techniques	Masking in audiology is the act of playing white noise into the non-test ear to prevent it from hearing the tones that crossover from the test ear. It helps to obtain the true threshold of the test ear and ensures that the non-test ear is not helping out.
Milestone Baseline	This means the initial audiometric value is determined at the first STS testing.
Monaural	Involves 1 ear.
Monitoring Audiogram	Monitoring audiograms are performed on employees who are exposed to noise levels equal to or greater than 85dB(A) in the mining industry. The objective of monitoring audiograms is to focus on the prevention of permanent hearing loss and to assess the effectiveness of the Hearing Protection Devices (HPD). The test is performed immediately after noise exposure to detect a temporary threshold shift when the worker presents for audiometry during medical surveillance.
Noise-Induced Hearing Loss	Noise-induced hearing loss begins at the higher frequencies (3000 to 6000Hz) and develops gradually as a result of chronic exposure to sound levels equal to or above 85dBA (continuous exposure to loud noise over an extended period, such as noise generated in an engineering workshop). Although the loss is typically symmetric, noise from firearms or sirens may produce an asymmetric loss. NIHL can be caused by a one-time exposure to an intense “impulse” sound, such as an explosion often leading to acoustic trauma. Recreational activities can also cause NIHL such as target shooting and hunting, listening to MP3 players at high volume through earbuds or headphones, playing in a band, and attending loud concerts. NIHL is 100% preventable.
Percentage Loss of Hearing	Percentage Loss of Hearing (PLH) is a reference value for the hearing status of an individual against which loss can be measured however PLH does not necessarily indicate hearing loss. Instruction 171 introduced a measure of impairment termed percentage loss of hearing (PLH) which is calculated by using a series of tables based on a summation of hearing loss in each ear at the following frequencies: 500, 1000, 2000, 3000 and 4000Hz (COIDA, 2001). The PLH forms the principal criterion for assessing hearing status for compensation claims⁹.
Percentage Loss of Hearing Shift	Is the change in the value of the PLH when compared to the reference value.
Periodic Audiogram	The Periodic Audiogram is performed either on an annual basis or every 6 months depending on the noise level the worker is exposed to.
Permanent Threshold Shift	PTS can be defined as a noise-induced threshold shift that persists after a period of recovery subsequent to the exposure. PTS is sensorineural and varies across frequencies, depending on the characteristics of the exposure, the transmission characteristics of the external and middle ears, and the innate sensitivity of different regions of the cochlea to damage.
Physiological	Refers to the normal functioning of the human body.
Pseudohypacusis	Pseudohypacusis is a condition in which hearing loss is exhibited in the absence of disease. The worker exhibits hearing loss but there is no disorder. Pseudohypacusis refers to false or exaggerated hearing thresholds “measured” due to a lack of co-operation from the worker.
Psychological	Refers to the mental and social well-being of a human.
Pure Tone Audiometry	Pure tone audiometry is a hearing test used to identify the hearing threshold levels of an individual, to determine the degree, type, and configuration of hearing loss and thus provide a basis for diagnosis and management. It is performed by presenting a pure tone (sound) to the ear through an earphone and measuring the lowest intensity in decibels (dB) at which this tone is perceived. It is the rapid measurement of the hearing measured against a predetermined limit of normality. Pure tone air conduction and bone conduction tests determine whether or not there is any hearing loss; what type of hearing loss it is; the frequencies that are affected (configuration); and whether hearing loss is unilateral or bilateral. Even though pure tone audiometry is a useful measure of basic hearing function, it does not indicate how well speech is received or understood.
Pure tone air conduction (PTAC)	A pure tone is a single sound using one frequency related to a one-decibel measurement, at a time⁵. Air conduction refers to tones presented through earmuffs, making use of air in the outer ear as a medium⁵.
Sensorineural Hearing Loss	Sensorineural hearing loss (SNHL) is a type of hearing loss in which the root cause lies in the inner ear or sensory organ (cochlea and associated structures) or the vestibulocochlear nerve (cranial nerve VIII). Sensorineural hearing loss (SNHL) is due to problems in the inner ear, also known as nerve-related hearing loss.
Speech Discrimination	A word recognition test (also called speech discrimination test) assesses a person's ability to understand speech from background noise.
Speech Perception	Speech perception testing is an objective way to assess hearing. SPT involves listening to sentences or words in quiet and in background noise while wearing hearing technology.
Sound pressure levels	Sound pressure level (SPL) is the pressure level of a sound, measured in decibels (dB).
Standard Threshold Shift	An average change in hearing of 10dB or more at the frequencies of 2000Hz. 3000Hz and 4000Hz in one or both ears, as compared to the employee's milestone baseline audiogram.
Stimulus	Presenting a tone or sound into the ear via an audiometer.
STS Reportable Level	A standard threshold shift is the average change in hearing of 10dB or more at frequencies 2000, 3000, and 4000Hz, in 1 or both ears as compared to the baseline milestone or audiometric zero. This change results in specific actions by the employer, safety representatives and healthcare providers in terms of the hearing conservation programme to prevent further changes in hearing. Therefore, the main aim of the STS regulation is the early detection and prevention of noise-induced hearing loss. An STS of equal to or greater than 25dB hearing loss at the same frequencies is reportable. Any STS equal to or greater than 5dB should be investigated.
Temporary Threshold Shift	A threshold shift is defined as a reduction in a person’s ability to hear. A Temporary Threshold Shift normally occurs after exposure to loud sound and is described as fatigue of the hair cells. Threshold shifts that recover to baseline levels in the hours, days or weeks following exposure are termed temporary threshold shifts (TTS).
Unilateral	One ear.

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