| What happens when my baby is tested? |
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There are two main types of testing: one is the Otoacoustic emission (OAE screen) and the other type is ABR (Auditory Brainstem Response) screen.
Otoacoustic emissions(OAE) The OAE test is the most commonly used as a screening test to see if there is a need to test a child's hearing further. It works on the principle that the cochlea of a hearing ear responds to a sound by making a quiet sound. A small earpiece, containing a speaker and a microphone, is placed in the ear. A clicking sound is played and if the cochlear is functioning properly the earpiece will pick up the response of the cochlea. This is recorded on a computer and tells the screener if the baby has a clear response or needs a second check. If there is no clear response after a second test the baby will be referred for an ABR (see below). The test is very quick and gives an immediate result. It is not uncomfortable or painful for the baby. Being referred after the OAE testing does not necessarily mean that there is a hearing loss. It can be difficult to get a response if the baby is unsettled at the time of the test, if the room is noisy, if there is fluid in the ear from the birth process, or if the baby is premature. Auditory Brainstem Response (ABR) Sound travels through the outer ear as vibrations. When it reaches the cochlea it is converted into an electrical signal. This travels along the auditory nerve to the brain, where it is processed into recognisable sounds. The ABR test works by checking that this signal passes along the auditory nerve when sounds are played. Before starting the test, the audiologist will place a headphone over each ear in turn, and they will also put small sensors on the child's head. The sensors will pass information about the signals that pass along the auditory nerve to a computer. Automated Auditory Brainstem Response (AABR) After referral from the OAE screen the child has an automated ABR. Sound is played into the ear at a set level. The sensors on the head pick up the brain's response to the sound. If there is a clear response no further checks are needed. This test only takes a few minutes if the baby is settled. Diagnostic ABR If there is no clear response from the AABR a fuller ABR is carried out. A series of sounds are played at different levels of loudness. The sensors will pass information about the signals to the computer. The audiologist will monitor and interpret this information and explain what the results mean. The ABR test can be used to gather information about a child's hearing levels for a range of sounds. You can obtain a booklet on screening and deafness (no. ESPP 11) on: www.deafnessatbirth.org.uk (Training for professionals working with deaf babies and their families)
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