There are various different ways to test hearing, depending on the age of the person involved and the type of hearing loss. The medical term for hearing tests is audiometry. Note: the information below is a general guide only. The arrangements, and the way tests are performed, may vary between different hospitals. Always follow the instructions given by your doctor or local hospital.
How do hearing tests work?
There are various types of tests that can be carried out to check how well you are hearing. They vary according to who is being tested and why. Babies are obviously not able to say when they have heard a sound, so special methods are used when testing babies. In children, the principles of testing may be the same; however, the way in which the tests are carried out may be varied to obtain the most accurate results. There are also additional tests which help to check how well the middle ear and the brain are working in the hearing pathway.
The most common tests of hearing are described below.
Testing newborn babies
The automated otoacoustic emissions (AOAE) test is a quick, simple and painless way to screen newborns for hearing loss. A small earpiece containing a microphone and a mini-loudspeaker is placed in the ear. The loudspeaker makes clicking sounds in the ear. These are passed to the fluid-filled chamber called the cochlea. If the cochlea is working normally, it responds by sending a sound back to the ear canal. This is detected by the microphone. The test is extremely sensitive so that even a slight hearing loss can be detected and if there is a good response then no further checks are needed.
Sometimes, the response cannot be detected when the test is done. This could be because of hearing problems but initially it is more likely to be due to other factors. This could be because the baby is unsettled, the room was noisy or there was some fluid left in the ear after birth. The test will usually be repeated and if there is still not a good response then it will be followed up with another type of test called an automated auditory brainstem response (AABR) test.
In an AABR test a small earphone plays clicks into the baby's ear. If the baby can hear the click, the electric signal in the hearing nerve on its way to the brain can be picked up by sensors that are placed on the baby's skin over their head. The loudness of the clicks is set to a particular level. If this does not produce a response, further different tests will be needed.
Both AOAE and AABR testing are best done when the child is asleep, as the response to be detected is very small and can be difficult to pick up if there is a lot of movement.
Testing in babies and young children
In young children a technique called visual reinforcement audiometry is used. In this test the child hears sounds, usually through speakers in the testing room. When the child hears the sound and turns their head towards it they are given a reward. Usually this is a visual reward such as the flashing lights of a toy. The person testing the child's hearing continues to reinforce this behaviour with a reward every time the child turns towards a sound. Then the person carrying out the test begins to assess the child's hearing by seeing if they respond to different types of sound. By doing this it is possible to find the quietest sound the child can hear.
Different variations of this reward-based test are used as a child becomes older and finds it easier to communicate.
Testing in older children and adults
In older children and adults testing mainly uses a technique called pure tone audiometry. This uses a machine called an audiometer to play a series of tones through headphones. The tones vary in pitch (frequency, measured in hertz) and loudness (intensity, measured in decibels).
The health professional conducting the test will control the volume of a tone and reduce its loudness until you can no longer hear it. Then the tone will become louder until you can hear it again. You signal by raising your hand or pressing a button every time you hear a tone, even if the tone you hear is very faint. The health professional will then repeat the test several times, using a higher-pitched tone each time. Each ear is tested separately.
The results of the test are plotted on a special graph called an audiogram which helps to show the pattern of any hearing loss.
What are hearing tests used for?
Hearing tests are used in a number of different circumstances including:
- To evaluate possible hearing loss in anyone who has noticed a persistent hearing problem in one or both ears or has had difficulty understanding words in conversation.
- When determining the type and amount of hearing loss (conductive, sensorineural, or both).
- Screening babies and young children for hearing problems that might interfere with their ability to learn, speak, or understand language.
- To screen for hearing loss in people who are repeatedly exposed to loud noises or who are taking certain antibiotic medicines, such as gentamicin.
What should I do to prepare for a hearing test?
Usually very little preparation is needed for a hearing test. If you are known to have wax in your ears you may have to have this removed before the test, so that it does not interfere with the results.
Let the person doing the test know if you have had, or the child being tested has had, a recent cold or ear infection, as this may interfere with the results.
Are there any side-effects or complications from hearing tests?
These are very safe tests; complications arising from these tests are extremely rare.
Further reading and references
; Audiometry screening and interpretation. Am Fam Physician. 2013 Jan 187(1):41-7.
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