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Building Blocks: Diagnostic Hearing Assessment in Infants A Matter of Time

McCreery, Ryan PhD

doi: 10.1097/01.HJ.0000436550.64508.31
Building Blocks

Dr. McCreery is an associate director of audiology and staff scientist at Boys Town National Research Hospital in Omaha, NE.



Infants who do not pass their newborn hearing screening need prompt and accurate diagnostic assessment to determine the need for amplification and early intervention services.

In practice, the process of assessing hearing in infants is complicated and fraught with challenges. Many of these challenges are new, since universal newborn hearing screening has only been widely available for a little over a decade.

The appropriate test protocols, timing of follow-up, and amount of information needed to make recommendations all must be considered. The purpose of this article is to help maximize information and minimize delays by discussing some of the more difficult aspects of clinical decision making in infant hearing assessment.

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Screening is distinct from diagnostic assessment; the result of a screening is either pass or fail and does not lead to specific recommendations. Professionals who assess infants must decide whether to do a full diagnostic assessment for every infant referred to their clinic or provide an additional screening.

Since the vast majority of infants who do not pass their newborn hearing screening have normal hearing, one can conclude that a diagnostic assessment for every infant who refers from newborn screening would be inefficient in terms of time and costs to the patient and healthcare system.

However, many pediatric clinics have extensive wait times for follow-up appointments, delaying the diagnosis of hearing loss if multiple appointments are required. Rescreening may be reasonable and efficient in some cases, but adequate time should be available to complete a diagnostic assessment if the rescreening cannot rule out hearing loss.

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Opinions about which protocol for infant assessment is best vary widely, from a standard protocol for every infant to adapted tests based on the information needed to rule out the presence of hearing loss.

At a minimum, the type of assessment used in the diagnostic evaluation should match the type of assessment used in newborn hearing screening.

For example, a baby who does not pass an auditory brainstem response (ABR) screening should receive at least an auditory brainstem response assessment as part of diagnostic follow-up.

In cases where the type of test used in newborn hearing screening is unknown, performing ABR for the diagnostic assessment is the safest approach to avoid missing cases of neural hearing loss or mild hearing loss.

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What order of tests gives us the most information? The answer to this question depends on the state of the infant and requires flexibility on the part of the clinician.

If the infant arrives to the appointment awake, clinicians may opt to start with tests that do not require the infant to be asleep, such as high-frequency tympanometry or otoacoustic emissions (OAE).

Unfortunately, the act of preparing infants for ABR testing requires scrubbing the skin and placing electrodes, which can upset infants or make them less likely to sleep.

Our clinicians will often place the electrodes for ABR and then have the parent or caregiver feed the infant to get the baby to sleep. ABR thresholds provide the most definitive data used to predict an infant's hearing status. Therefore, obtaining ABR thresholds at multiple frequencies in each ear is the top priority for our clinicians.

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How much information is needed to call the results “normal” and dismiss the child from audiological care? Ideally, the clinician should be able to document levels equivalent to normal hearing at a high and low frequency in each ear.

In cases where rescreening is completed instead of a diagnostic evaluation, information is usually only obtained in the high frequencies (> 2,000 Hz), either with OAEs or with click or high-frequency tone-burst ABR thresholds. As a result, a “pass” on a high-frequency rescreening is unlikely to miss a low-frequency hearing loss that would not already have been missed by the original screening.

However, professionals should be specific about the frequency range assessed, as well as what information might be missed when using rescreening instead of a diagnostic evaluation.

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Many of the infants we see for follow-up after newborn hearing screening have abnormal high-frequency (1,000 Hz) tympanometry, consistent with middle ear fluid or dysfunction.

This situation raises two important questions: Should further testing be completed when evidence of middle ear dysfunction exists, and how soon should follow-up testing be recommended in cases of middle ear dysfunction?

Although clinicians have different opinions on the issue, I tend to operate under the assumption that I may not have another opportunity to test the infant, and I usually perform a diagnostic assessment with auditory brainstem response to determine the extent of hearing loss present with middle ear dysfunction.

Although the threshold information may be confounded by the middle ear problems, my counseling with the family about follow-up would be more urgent if the results showed thresholds in the severe-to-profound range instead of the mild-to-moderate range anticipated with middle ear dysfunction.

The timeline for follow-up depends on the ABR threshold data, but follow-up should be attempted as soon as possible to avoid the likelihood that the infant will reach an age where natural sleep assessment is no longer possible, and anesthesia may be necessary to perform ABR testing. It is important to recommend medical management with otolaryngology or the child's primary care provider in these instances.

The diagnostic assessment of infants after referral from newborn hearing screening is a critical first step in the process of identifying hearing loss. Making clear and decisive recommendations about the timeline for follow-up assessment can help families understand the information being provided and the next steps needed for their child.

© 2013 by Lippincott Williams & Wilkins, Inc.