Infant Hearing Screening : Failing Hearing Tests
Handling Failed Hearing Test Results in Neonatal Hearing Screening
Oct 28, 2009
Between 2 and 10 percent of all newborns fail hearing tests in the infant hearing screening program, but less than 1 percent turns out to have permanent hearing loss. There is a 1 in a 1000 chance of a baby being born with severe hearing problems and the hearing screening programs have been designed to identify just those infants. But there are several reasons why even an infant with normal hearing could fail these tests.
Hearing Tests used for Infant Hearing Screening
Newborn hearing screening programs commonly use two tests, Otoacoustic Emissions (OAE) and Auditory Brainstem Response (ABR), both of which are noninvasive and can be performed quite painlessly while the baby rests quietly.
Otoacoustic Emissions (OAE) – This test uses a small probe inserted into the ear to detect echoes produced by the inner ear in response to sounds and is good for detecting any blockage in the ear canal, fluid behind the ear drum and any problem with the cochlea.
Auditory Brainstem Response (ABR) – Electrodes placed on the head record electrical activity in the nerve for hearing and the brain in response to sounds. This test can locate problems in the inner ear, the auditory nerve and the hearing centre in the brain.
Both tests take between 5 and 15 minutes to complete and are reliable screening tools. Hospitals choose one or the other for reasons like cost and availability of trained personnel and not because one is better than the other. The two tests are in fact complementary to each other and for in depth analysis of hearing loss both have to be performed.
Interpretation of the Hearing Tests in Infant Hearing Screening
Both tests use computers to compare the newborn’s response to standard responses and give a pass or fail report. A “fail” does not declare the baby to be deaf, it only says the baby has to be tested again at a later date. Sometimes, even an infant with normal hearing can fail the test. This usually happens when there is amniotic fluid (fluid from the birth) blocking the ear canal. There may also be fluid behind the ear drum. These block sound waves from reaching the cochlea, giving a negative result. A crying and irritable baby can also cause the result to be negative.
Between 2 and 10 percent of all newborns fail the test, but less than 1 percent turns out to have permanent hearing loss. The false positive rate (the percentage of infants who have normal hearing but fail the test) is about 4 percent for ABR and between 5 and 21 percent for OAE. The rate may be higher for OAE because it is more affected by the presence of residual amniotic fluid in the ear canal.
Causes for Failure in Hearing Tests During Infant Hearing Screening
These depend on the test used for screening, but overall they can be summarized as follows:
- Residual amniotic fluid or vernix in the ear canal
- Fluid behind the ear drum
- Debris in the ear canal
- Excessive noise or movement of the baby
After Failing a Hearing Test
An infant who fails the test is generally given a date for a repeat test. Remember that failing the screening test does not necessarily mean that the infant has a hearing loss, it only says the baby has to be tested again. Either way it is very important to take the baby back for a second screening test.
Things to remember during retesting:
Allow a gap of at least one week between the two tests. If the cause of failure was fluid in the ear canal or the middle ear, it has to dry before the second test. Make sure the baby rests quietly during the test. Feeding the infant just before the test may ensure that.
Sources:
Gleeson, Michael J. Scott-Brown's Otorhinolaryngology: Head and Neck Surgery. Oxford University Press; 7 Edition, 2008.
