Hearing testing and screening in young children

Introduction

About 1,300 children born in the UK each year have permanent hearing loss in one or both ears of moderate or worse severity.¹

About 50-60% of people with hearing loss have a genetic aetiology; the remaining 40-50% of cases are attributed to environmental factors such as ototoxic drugs, prematurity, or trauma.²

The Newborn Hearing Screening Programme was introduced in the UK in 2006, replacing the previous infant screening programme (the 'distraction test' at 8 months). Most congenitally deaf children are now identified and managed appropriately before 6 months of age. Identification of permanent hearing impairment at the earliest possible age is crucial to maximise the development of speech and language.

Rationale for screening¹

• Universal newborn hearing screening identifies the majority of the 1 in 1,000 children born with a hearing impairment.

• Hearing loss is not confined to those with risk factors - approximately 40% of all children ultimately identified with sensorineural hearing loss do not have an established risk factor; therefore, universal screening is recommended.

• Hearing screening allows hearing loss to be identified at a younger age. There is good evidence that this is beneficial because early detection and management improve outcomes in terms of speech, language and education.^{3 4}

• The critical age for commencing intervention may be as early as 6 months.

• Parents may quickly recognise a baby as having severe or profound hearing loss; however, moderate hearing loss or high-frequency hearing loss may go unnoticed for several years unless formally tested.

Screening tests for hearing loss¹

The coverage and newborn hearing screening uptake across England is around 98%. Although the vast majority of babies pass the test, around 2% of babies are referred to audiology services for further assessment.

Neonatal hearing screening tests

Automated otoacoustic emissions (AOAE) test

• The AOAE test measures the integrity of the inner ear.

• It works on the following principle:
  

  • In the healthy cochlea, vibration of the hair cells in response to noise generates acoustic energy, known as otoacoustic emissions. A probe is placed in the ear canal and generates wide-band clicks. Acoustic energy produced in response to the clicks is detected by a microphone within the probe.

• AOAE screeners display the results of the test as either pass or refer, requiring no test interpretation by staff.

• The test takes a few minutes.

Automated auditory brainstem responses (AABR) test

• The AABR test measures not only the integrity of the inner ear but also the auditory pathway.

• It can therefore detect the rare condition of auditory neuropathy in children who are deaf but have normal otoacoustic emissions (because the cochlea is normal).

• The stimulus (either clicks or tones) is presented using earphones or an ear canal probe, and the electrophysiological response from the brainstem is detected by scalp electrodes. Automated devices allow screening to be performed by non-specialists.

• This test takes 15 minutes.

Test limitations

• Both tests require a quiet baby and a quiet environment.

• Debris in the canal or middle ear fluid can affect the tests (including amniotic fluid in the ear canal following birth).

• Only the AABR test will detect auditory neuropathy (where the cochlea is normal).

• Neither test will detect central hearing impairment (where hearing loss is secondary to dysfunction of the pathways from brainstem to auditory cortex).

Current screening protocols in the United Kingdom¹

Newborns

Well baby protocol:

• For babies who had no requirement for special care (or <48 hours in special care).

• Uses the AOAE test. Babies not passing this test are given the AABR test.

Neonatal intensive care/special care baby unit protocol:

• Uses both AOAE and AABR tests. The latter can detect auditory neuropathy, which is more common in special care babies.

Then:

• If these tests are not 'passed', babies are referred for audiological assessment within four weeks of screening or when the baby is 44 weeks of gestational age.

• If there are risk factors requiring surveillance, refer for continued audiological assessment at 7-9 months of age.

School entry hearing test

• Currently, this is performed in most areas of the UK.

• Later-onset hearing impairment can occur at any time and there is no optimum time for further screening.

• The test used is the 'pure tone sweep test' which is pure tone audiometry.

• Following the introduction of newborn screening, most cases of hearing impairment will be identified before school entry; however, there will be some cases that were missed or have developed after the test.

• This non-standardised school entry screening (SES) programme which is in place in many parts of the UK, is of questionable value.⁵

Further hearing tests in children

Various tests can be performed by the audiological service, depending on the age of the child and the level of co-operation. For example, in the 'toy test' the child points to toys named in a low voice by the tester. Pure tone audiometry is used with older children who can co-operate.

Visual reinforcement audiometry (VRA) is now used in preference to distraction testing. The test is a behavioural test which can be carried out with young children between the developmental ages of 7 months and 3 years.

Awareness and referral during childhood⁶

See also the article on Deafness in Children.

Even if the hearing screening tests have been 'passed', parents and carers should continue to be vigilant for signs of hearing loss. This is because:

• Hearing loss may develop later.

• Some children may have missed out on screening programmes - eg, new immigrants.

• Some hearing loss may be missed on screening.

• High-frequency loss may not be obvious to family and carers but will nevertheless impair understanding of speech.

Symptoms of hearing loss

The child may be:

• Inattentive, not reacting when called.

• Talking too loudly, listening to TV at high volume.

• Mispronouncing words.

• Unsettled at school.

• Tired, grumpy or overactive.

• Demonstrating difficult or withdrawn behaviour.

Who should be referred for audiology assessment?

Referral criteria will vary slightly with local service provision but the following is a guide:

• Those children who did not pass the screening test.

• Those children who missed their screening test.

• Babies with the following risk factors, who should be considered for referral for targeted follow-up, even if they pass the screening tests:

  • High risk of middle ear problems: syndromes associated with hearing loss (eg, Down's syndrome, Turner syndrome), cleft palate, other craniofacial abnormalities (eg, atresia/microtia of the ear canal; chromosomal or syndromic conditions, branchial arch and cervical spine anomalies).

  • Congenital infection due to toxoplasmosis, rubella or cytomegalovirus.

  • Had special care for >48 hours, and no clear response to AOAE in both ears despite clear response on AABR.

• Babies with the following risk factors should be referred to Audiology for assessment:
  

  • Any parental or professional concern.

  • Confirmed or strongly suspected bacterial meningitis, or meningococcal septicaemia.

  • Temporal bone fracture.

  • Severe unconjugated hyperbilirubinaemia.

• Children with delayed speech and language may also require referral.

• After treatment with ototoxic drugs (eg, aminoglycosides), they should be referred only at the discretion of a paediatrician.

• Any parents who express concerns about hearing despite the screen should always be referred to Audiology.