An infant is sleeping or sedated for the ABR. An infant may be sleeping naturally or may have to be sedated for this test. Additionally, older, cooperative children may be tested in a silent environment while they are visually occupied. Tiny earphones are placed in the baby’s ear canals. Usually, click-type sounds are introduced through the earphones, and electrodes measure the hearing nerve’s response to the sounds. A computer averages these responses and displays waveforms. Because there are characteristic waveforms for normal hearing in portions of the speech range, a normal ABR can predict fairly well that a baby’s hearing is normal in that part of the range. An abnormal ABR may be due to hearing loss, but it may also be due to some medical problems or measurement difficulties.
What is an ABR test?
Your child has been scheduled for an auditory brain stem response (ABR) test. This is a way to measure how well each ear can pick up sounds and how well the hearing nerve sends the information to the brain. The test does not require that children tell or show that sounds are heard. It is commonly done on infants and small children, or anyone who cannot or will not cooperate with routine testing.
Before the Test:
Your child will need to be asleep for the test. So that he/she may fall asleep easier, please remember the following:
- Your child may eat or drink before the test. However, he/she should not have any caffeine — including chocolate and cola drinks — for at least 12 hours before the test.
- It is strongly advised that your child avoid taking a nap before arriving for the test.
During the Test:
If your child is 6 months of age or older, he/she will be weighed and may be given a mild medicine by mouth to make him/her sleepy. The skin on the forehead and behind each ear will be cleaned off and small surface electrodes (disks) will be taped on those areas. The wires from the discs are then attached to a special computer.
Once the child is asleep, small earphones will be placed in the ears. Sounds will be presented through the earphones. Brainwave activity will be obtained using the computer. These waveforms are then analyzed to determine whether or not the ears are detecting the sounds.
After the Test:
When the test is finished, your child will be awakened. The audiologist (a specialist in hearing healthcare) will discuss the test results and any necessary recommendations. A written report will be sent to your child’s doctor who will also discuss the results with you.
Unlike a hearing evaluation, which evaluates how well you hear sound, an auditory brainstem response test (ABR) evaluates how well the sounds travel along the hearing nerve pathways to a particular part of the brain called the brainstem.
An ABR may be recommended for a variety of reasons. It can be used to estimate the sensitivity of the ear to sound, such as in the testing of newborns, older children who cannot perform well on a regular hearing test, or even adults who are unable to accurately complete a regular hearing test.
For adults, the most common reason an ABR is recommended is to help eliminate the possibility of a disorder along the hearing nerve or in the brain itself. Sometimes, such problems can mimic a typical hearing loss; fortunately, your audiologist has the skills, knowledge and experience to recognize hearing test findings that suggest there may be more to the hearing loss than meets the eye.
To complete the ABR test, electrodes are pasted and taped to the scalp and earlobes and soft foam tips are inserted into the ear canals. Clicking sounds then are delivered through the ear tips at a comfortable-to-fairly-loud level. These sounds cause nerve responses that are picked up by the electrodes and passed on to sophisticated equipment to record these responses. Your audiologist can then measure the responses to determine if they are normal or abnormal. The results are then delivered to your physician so he or she can evaluate any possible need for further medical evaluation.