Hearing tests

How do hearing tests work?

There are various types of deafness 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 for a baby's hearing test.

• In children, the principles of testing may be the same; however, the way in which the tests are carried out may be varied to get 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, there is background noise 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 visual reinforcement audiometry test is used. In this test the children hear 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.

Free hearing tests are readily available online. An online hearing test often involves listening to a tone through the earphones you may usually use to listen to music on your laptop or computer. They will only provide a rough assessment of your hearing but may be useful if you are not sure whether you need a face-to-face assessment or not.

Free hearing tests are also available on the NHS via a GP referral but you may have to wait a few weeks for an appointment. You may find it quicker to book a hearing test at a large pharmacy or optician, but you will still need an NHS assessment if you need a hearing aid and want a free one.

You should in any case consult your GP if you have other symptoms such as earache or discharge, or sudden hearing loss in one ear.

A face to face assessment will take around 60 minutes the first time you go. Follow-up appointments usually take around 45 minutes.

Babies born in the UK will be offered a hearing check sometime in their first 3 months. If you are concerned that there may be a problem with their hearing, you need to observe how they respond to sound around the home. For example, does the baby startle at unexpected loud noises or quieten when they hear the voice of their usual carer?

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.

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.

These are very safe tests; complications arising from these tests are extremely rare.

Adult audiogram tests cover the full range of sound frequencies, so they can be very reliable as long as you are honest about whether you can hear the sound. Don't click the button if you haven't heard the sound.

Online hearing tests are less accurate and only give an indication of whether there might be a problem that you should have checked out by a health professional.