Early Hearing Detection and Intervention (EHDI) programs are designed to identify infants with hearing loss by the time they are 1 month old so that their hearing loss is diagnosed and defined no later than 3 months of age.  When hearing loss is identified early, babies can be enrolled in appropriate early intervention programs (including being fit with hearing aids) by 6 months of age or younger.  When infants with hearing loss are diagnosed early and enrolled in early intervention, they have positive speech, language, and listening outcomes regardless of communication modality.

When should a Diagnostic Audiological be performed?

Diagnostic Audiology occurs after a baby fails to pass a follow-up rescreen, between 1 and 3 weeks of age. The diagnostic evaluation should occur between the ages of 1 month – 3 months of age. 

Some key Components in Diagnostic Audiology of infants and children are:

Pediatric Audiologist: 
Infants who are referred from newborn hearing screening should have an initial audiological evaluation by a pediatric audiologist to determine the type (where the hearing loss exists), degree (how much hearing loss exists) and configuration (frequencies or pitches that are affected) of the hearing loss.   A Pediatric Audiologist is an individual who is trained, has a masters, doctorate or PhD in Audiology and has the technical expertise and desire to work with the infant population.  The Audiologist performs an audiological test battery to include physiologic measures and developmentally appropriate behavioral techniques.

Case History Documentation:
It is important that the audiologist has complete information about family history of hearing loss, conditions that occurred during pregnancy including maternal illnesses, complications that occurred during labor or delivery, and time the infant spent in the neonatal intensive care unit (NICU).    This information helps the audiologist determine if there are any pre, peri- or postnatal conditions that may be related to hearing loss.  When an infant is referred from the newborn screening, but a hearing loss is not diagnosed the case history may provide information that indicates that he/she is at risk for a progressive or late onset hearing loss. (See JCIH Risk indicators, appendix A)

Auditory Brainstem Response (ABR):
 ABR is an electrophysiological measurement that allows the audiologist to obtain information about the condition of the inner ear and/or auditory nerve.  It is an accurate and reliable predictor of hearing loss in infants and young children, therefore, the degree and type of hearing loss as well as the configuration can be determined with ABR, even in very young infants.  Since very young infants (less than 6 months old) cannot provide information about their hearing through behavioral testing, ABR is the most critical procedure in the initial test battery.  ABR should include Clicks, Tone bursts, and Bone Conduction testing.

Auditory steady state responses (ASSR):
ASSR measurements are also a diagnostic tool for evaluating frequency-specific thresholds.  It is also an electrophysiologic test that uses electrodes.  The benefit of the ASSR is that the results may provide more specific threshold information for infants who have severe to profound hearing losses.  This enables the audiologist to have more precise data to proceed with hearing aid fittings or determining cochlear implant candidacy.  At the present time ASSR is not available in all audiological clinics. It should also be noted that the Joint Committee on Infant Hearing (JCIH) 2007 Position Statement does not recommend this procedure to be the sole measure of auditory status in newborns and infant populations.  JCIH report that there is insufficient evidence to support using this procedure as the only electrophysiological test.

Sedation: Generally, infants less than 6 months of age do not need sedation.  When sedation is needed the ABR may occur in a hospital operating room or a special clinic room.  In either case, a physician must be on site and a medical professional must monitor the infant’s vital signs while the audiologist is performing the ABR. Techniques for preparing an infant for ABR (with and without sedation) are displayed in Appendix B.

Otoacoustic Emissions (OAE): 
OAEs are small sounds caused by motion of the eardrum in response to vibrations from deep within the cochlea.  The healthy cochlea creates internal vibrations when it processes sound – an impaired cochlea usually does not.  OAEs are not present when an infant/child has a sensorineural hearing loss of 30dBHL or greater.  It is important to note that conditions in the middle ear can make it difficult to measure OAEs.  Middle ear fluid or negative middle ear pressure associated with otitis media may eliminate all or part of the OAE.  The condition known as “auditory neuropathy / dys-synchrony” is diagnosed by comparing OAE (typically normal) and ABR (typically abnormal) results. Click here for additional information regarding OAE screening.

Acoustic Immittance Audiometry: 
Tympanometry is an examination used to test the condition of the middle ear and mobility of the eardrum (tympanic membrane) and the conduction of the middle ear bones, by creating variations of air pressure in the ear canal.  When tympanometry is used with very young infants their small, soft ears may affect the test and give inaccurate results.  Therefore, the pediatric audiologist must have specialized equipment that allows the use of a high frequency probe tone The high frequency probe tone is routinely used to increase the reliability and accuracy of tympanometry measure in the age group of 0-6 months of age. Click here for additional information regarding tympanometry.

Behavioral Audiometry: As a child matures and is able to provide hearing results behaviorally, the audiologist is able to plot hearing information.  During audiological testing, the audiologist finds the lowest intensity level at which a child just detects sounds (threshold) at different frequencies.  The audiologist uses audiograms (a graphic representation of hearing loss) to determine the degree of hearing loss and classify it as mild, moderate, moderately severe, severe, or profound.  Visual reinforcement audiometry can be effectively used with infants as young as 6 months. A confirmatory audiologic test battery for infants and toddlers age 6 through 36 months should include this procedure in addition to the components previously mentioned. (This procedure assesses the infant/child’s behavioral response to auditory stimuli in a sound proof booth.)

In Visual reinforcement audiometry (VRA), a baby is trained to turn toward a toy (one that lights up and/or moves) when he/she hears a sound.  When this testing is used, a complete audiogram can be obtained.  Individual ear air conduction and bone conduction thresholds can be measured at all typical clinical frequencies (250, 500, 1000, 2000, 4000, 8000 z) or at low, mid, and high frequencies (target audiogram). 

After about 2 years of age, a baby can be trained for conditioned play audiometry (CPA).  In CPA the child “plays a game” to show that he/she has heard a sound.  The audiologist teaches the child that when he/she hears a tone, he can drop a ball in a bucket (or some other enjoyable activity).  CPA usually results in a complete individual ear audiogram by both air and bone conduction.  The key is to keep the child interested in the task.

Click here for additional information regarding audiograms and bone conduction hearing.

Audiological Monitoring:  Although universal newborn hearing screening is designed to identify infants who have congenital hearing loss, it is important to acknowledge that some infants are born with progressive or late-onset hearing losses.  If a child has unilateral, mild, or chronic conductive hear loss or is “at risk” for progressive or delayed onset hearing loss, ongoing services should include audiologic monitoring.

“All infants with a risk indicator for hearing loss (Appendix A), regardless of surveillance findings, should be referred for an audiological assessment at least once by 24 to 30 months of age. Children with risk indicators that are highly associated with delayed-onset hearing loss, such as having received ECMO or having CMV infection, should have more frequent audiological assessments.” (JCIH, 2007)