Neonatal otoacoustic emission screening and the

Neonatal otoacoustic emission screening and the

F16

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Archives of

Disease in Childhood

1996;

74:

F16-F25

Neonatal otoacoustic emission identification of deafness screening and the

P M

Watkin

Audiology Services,

Forest Healthcare,

Whipps Cross

Hospital, Whipps

Cross Road,

Leytonstone, London

Ell 1NR

P M Watkin

Correspondence to:

Dr P M Watkin.

Accepted

1995

28 September

Abstract

Using transient evoked otoacoustic emissions

(TEOAEs), a two stage screen with the testing of failures by auditory brainstem response (ABR), has been implemented in Whipps Cross Hospital in East

London. From January

1992 to

1995,

11%606 infants received an initial TEOAE test.

Once initial difficulties were resolved, coverage of district residents remained stable at 91 5%.

Long term follow up of the cohort is being undertaken. Of those receiving an initial test, 13% failed in both ears.

Only

1.75%

of the cohort failed both stages

These of the TEOAE screen bilaterally.

infants were tested by ABR. The yield of infants with a bilateral permanent hearing loss of moderate or worse degree was

2/1000.

The overall cost of implementing the programme was not

prohibitive

and the cost per hearing impaired child detected was little more than the

widely

accepted notional cost of identifying such children through targeted at risk screens.

The screen was clearly sensitive. The priority for such universal TEOAE programmes, however, is to increase specificity without losing this

sensitivity.

(Arch Dis Child 1996; 74: F16-F25)

Keywords: transient evoked otoacoustic emissions, screen, hearing loss, costing.

The identification of congenital hearing impairment early in infancy is accepted as an important and appropriate aim of health service provision. To this end screening the hearing of all neonates has been recommended in the USA

by

the National Institutes of Health.

I

Transient evoked otoacoustic emission screening (TEOAE) in the maternity unit, with testing of failures by auditory brain stem response

(ABR), was recommended by the consensus

panel.

ABR auditory is an established and sensitive test of function,2 but the standard procedure is time consuming and requires a high level of audiological skill. Thus the initial screen recommended by the NIH was the recording of TEOAEs. These acoustic responses associated with the normal hearing process had

originally

been described at the Institute of

Laryngology and Otology, London, by

Kemp,3 and his further development, by 1987, of simple, quick, and non-invasive clinical recording techniques made universal screening a possibility.4

Reservations about the

practicability,

cost, and effectiveness of such universal TEOAE screens were quickly expressed in the USA.5

Although there are obvious advantages in screening within the maternity unit, Haggard6 had already pointed out the logistical difficulties, cautioning that the main obstacle to credible screening is the swamping of available assessment facilities with false positive results.

Just over half of neonates are discharged from maternity units in

48

England

and Wales within hours (Department of

Health, personal communication).

Unfortunately, low pass rates with

TEOAE screening are achieved within this

period.7-9

Thus it may not be practicable to implement the programme recommended by the NIH in the United

Kingdom.

Although in most of the districts in this country a universal screen using the distraction test in the latter half of infancy is already in place, and many districts also selectively screen neonates, the results are variable and thus universal neonatal hearing screening has already reached the agenda.o1

11 Most parents of deaf children would have welcomed neonatal identification, a recent study

shows.'2

This report details the introduction of a universal neonatal TEOAE screen in the East

London district of Waltham Forest.

A universal infant distraction test has been in place within the district since the

1

970s, with a selective at risk neonatal screen being introduced in

1986.

However, only 43% of the deaf children in a cohort from the district were identified by the selective screen.13

Although the infant distraction test was considered sensitive, the mean age of identification for those with congenital deafness remained at over

1

year.'4

To further reduce this, a universal TEOAE screen of infants within the first 3 months of life was introduced in January

1992.

The implementation of the screen followed a pilot study undertaken the previous year.

The screen aimed at

identifying

infants with congenital or early onset bilateral permanent hearing impairment of moderate or worse a

degree.

It was

acknowledged

that mild degrees of hearing impairment as well as unilateral congenital deafness and middle ear disease may result in disability.

However, it was considered that those targeted by the screen would probably most benefit from the earlier provision of

multidisciplinary

habilitation. The selective neonatal screen was replaced by this universal screen.

The

infant

distraction test undertaken by the health visitors, and other surveillance methods established over many years in the district, were left in place.

Evaluation of the screen processes, outcome, and cost has been ongoing since 1992.

The results of this three year evaluation to

1995 are presented here.

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Neonatal otoacoustic emission screening and the identification of deafness F17

Table 1 TEOAE result scoring criteria

Response

(a) present if all criteria met (pass)

Response present at higher intensity than noise derived from subtraction of both averaged waveforms

(b)

(c)

Overall correlation of both averaged waveforms >50%

Correlation of both averaged waveforms at 3 of the bandwidths from 1-6 kHz, 2-4 kHz, 3-2 kHz, and 4 0 kHz

>50% with one >75%

(d) Bandwidth signal to noise ratio ¢5 dB in all 3 selected bandwidths with signal to noise ratio

-

10 dB in at least two

Borderline response in all

(a) from

Response present at subtraction criteria met higher intensity of both averaged than noise waveforms derived

(b) Correlation of both averaged waveforms and/or bandwidth signal to noise ratio does not meet pass criteria

(c) Bandwidth signal to noise ratio

-

10 dB in two of the bandwidths

No response

(fail)

(a) Even if a response is present if the bandwidth signal to noise ratio does not meet the criteria for a 'borderline'

no response scored

Methods

Waltham Forest is an

East London

borough

with a population of 220 000.

It ranks 20th lowest out of all local authorities in England and Wales in terms of social and economic

deprivation.

Paediatric and maternity services and the special care of neonates are provided by Whipps Cross Hospital. Around

3500 babies are born each year to residents of the district.

Around 85% are born in Whipps

Cross and the remainder in neighbouring or central London

maternity

units.

A very small number of births are by home delivery.

Additionally, around one quarter of babies delivered in Whipps Cross are to residents of neighbouring districts. All required inclusion in the hearing screening programme.

TEOAE TEST

The recording of TEOAEs was done by the commercially available Otodynamics ILO88.

This system has been described in detail else-

where,15

16 and typical results illustrated.17 18

The

IL088

was used in default mode with the derived non-linear cochlear emission collected.

The emission recording was made 2-5 milliseconds after

stimulation,

and initially a time gate up to 20 ms was used. With the avail-

ability

by 1993 of the

IL088 'QuickScreen',

the sweep time was reduced to 12-5 ms.

Click stimuli of

80 ,us

rectangular pulses

with

peak

stimuli kept near to

80 dBSPL were presented

through

a

Knowles magnetic transducer inserted into the external auditory meatus.

The emission was recorded

through

a transducer

placed

within the same

probe

in the ear.

The

IL088

system collects two

independent averaged

emission waveforms for each test and these are frequency then used for cross comparison and

analysis.

The cross power spectrum of the two waveforms is calculated and dis-

played

for

frequencies

from 0-5 kHz. The frequency spectrum of the difference between the waveforms measures noise contained in the waveform.

The response signal to noise ratio for specific and also frequency bandwidths graphically displayed is calculated from 0-5 kHz.

The two emissions collected at the end of the test are also cross correlated both as the complete waveform and at

The specific frequencies.

intensity of the reproducible components of the waveforms is also computed as the emission intensity in dBSPL units. The analysis is updated throughout the test, as is information about noise, stimulus, probe fit and test progress. This allows for repositioning of the probe or termination of the test as required by the tester.

The procedures and criteria for evaluating test results were standardised for all the testers.

Although the analysis software was updated with improvements made by Otodynamics, the criteria were equivalent throughout the three years.

The ear tested first was that which was most accessible. The ear canal was not cleared of debris, but if a weak initial stimulus was obtained the probe was cleaned and refitted.

The TEOAEs were scored by the screener as response present, no response, borderline response and not possible to test.

The response criteria are shown in table

1.

Those ears with no response, a borderline response, or not possible to test were considered screen fails.

The screeners were test if a allowed to terminate the clear response was present, but only after at least 60 data samples had been collected. If there was no response the test was terminated after

260 data samples had been averaged.

The TEOAE recordings were made by neonatal hearing screeners newly employed as basic grade or senior assistant technical officers.

a

Training in the use of the IL088 was given over period of several weeks by the audiologists.

The screeners were also taught to interpret the test results and discuss them with the parents.

The results were entered on a database and also detailed in the parent held child health record books.

Samples of the TEOAE recordings and the screeners' decisions were evaluated weekly, with a hierarchical system of

checking

senior screener and audiologists.

by the

ABR TEST

The ABR test was undertaken by an experienced

audiologist.

Standard silver chloride electrodes were attached to the forehead and the ipsilateral and contralateral

Blue Tak and

mastoid,

with

Netelast.13

Using

a Medelec

Sapphire machine,

an

alternatively

inverted click stimulus was

presented

at a rate of

30 pps

through

a standard TDH39

headphone

held at the

baby's

ear.

The

analysis

time was

10 ms and the filter bandwidth was 200-2000 Hz.

The threshold was obtained for each ear by obtaining two repeatable waveforms acquired after a minimum of 1000 clicks.

SCREEN

A summary of the screen is illustrated in fig

1.

The initial test.

was

by

TEOAE

recording,

undertaken in a small non-soundproofed room dedicated for hearing screening within the maternity unit. The baby was kept in the cot without additional sound attenuating measures.

Before the test, each mother was given an explanatory leaflet. The initial test was undertaken whenever possible before discharge, but

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F18 Watkin

Neonates of Waltham

Forest residents not born at Whipps Cross Hospital

All neonates born at

Whipps Cross Hospital maternity unit surveillance, parental questionnaires, and an infant distraction test at 7-9 months.

Not tested with TEOAE before discharge

Identified from computerised birth notification at 4 weeks

Appointed in audiology department for TEOAE screen

All failing initial TEOAE test in both ears and unilateral fails requesting a retest

Appointed for Retest with TEOAE in audiology department

All failing Retest TEOAE in both ears and unilateral fails requesting an ABR

Threshold ABR within

4 weeks of retest

Figure 1 Flow diagram of neonatal screen.

Tested with

TEOAE before discharge as near to the time of discharge as possible.

Those admitted to the special care baby unit were tested once they had moved to the low dependency part of the unit.

Those failing the initial test in both ears were sent an appointment for a retest within the audiology department of the hospital. The parents of those passing in one ear were given the choice of

returning

for a retest.

Attempts were made to trace and test retest defaulters when the initial test had been failed bilaterally, but there was no coercion for unilateral failures. Those missed on the maternity unit, and those district residents born elsewhere, were given appointments for an initial test to be undertaken within the audiology department of the hospital. Their details were obtained

4 weeks after birth from an interactive computer system detailing district births. The time lag allowed for all neonates to have been entered on the system. Babies

moving

into the district after 4 weeks of age were referred into the programme at the time of their entry on to the district computer

3 system, with screen entry months of age.

being

offered up to

The initial test and retest were by TEOAE recording, with retest failures being referred for an

ABR.

If there were clear risk factors for deafness, parental concern, or delayed screen entry, failure at the initial TEOAE recording was followed by an ABR without a TEOAE retest. All babies referred for ABR were followed up by the audiology department. Screen passes entered the community health service hearing screening programme with hearing

EVALUATION OF THE SCREEN

The combination of the initial TEOAE test, the TEOAE retest, and the ABR examination were considered to constitute the screen.

Although the ABR examination was undertaken to threshold by an experienced audiologist, full audiological assessments were not carried out until the infants were referred into the diagnostic and rehabilitative clinics following the ABR.

The ABR examination was thus included as a component of the screen in the evaluations undertaken.

Coverage of the screen was measured as the number of infants tested as a percentage of those babies recorded on the district's child health interactive computer system as having been born to residents of the district or born in

Whipps Cross Hospital. Those becoming district residents up to 3 months from the date of birth were included. Those requiring and receiving each component test of the screen were enumerated.

Defaulters of the retest and

ABR were considered not to have been screened for calculation of coverage. Because the aim of the screen was the identification of bilateral hearing impairment, the retesting of unilateral

TEOAE fails depended on parental decision.

Thus only those failing the test bilaterally and not attending for the subsequent test were considered to have reduced the coverage.

The crude test failure rates of the initial TEOAE and retest were also calculated.

The yield was calculated from the ABR threshold in dBnHL obtained from the better ear.

However, this may be misleading as such infants often have a hearing loss attributable to middle ear effusions.

Such infants were not the target of the screen, and thus the yield of infants with a bilateral permanent hearing impairment of moderate or worse degree in the better ear was also enumerated. The infants were considered to have this impairment if the diagnostic audiological assessment confirmed average hearing thresholds in the better ear to be worse than 40 dBHL (or equivalent in other dB scales).

The cost of each test undertaken was

computed

from the cost of

equipment

and staff with

equipment

amortised over five years.

Costs of disposables for the TEOAE tests and

ABRs were included as was the cost of stationery. The cost for each test included the cost of clerical support and the cost of

retesting

the initial TEOAE failures and of undertaking the ABR examinations.

The costs of audiological assessments undertaken on those referred into the diagnostic and rehabilitative clinics

following

the ABR were excluded.

Overheads such as

lighting, heating,

and room costs were also excluded.

Results

RECIPIENTS OF THE

INITIAL

TEOAE TEST

During the three year period of the evaluation,

14 353 babies were enrolled for the screen. Of these, 9850 (69%) were district residents born

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Neonatal otoacoustic emission screening and the identification of deafness

F19 at

Whipps Cross Hospital. Another

2832

(20%) were born at the hospital, but were not residents

1618 of Waltham Forest.

Additionally,

(11%) Waltham Forest residents were born outside the district or by home delivery, and a small number (53) were included although they were neither born in the district nor resident.

Investigation of this small number demonstrated that they were incorrectly identified as residents, or were staying with relatives.

Out of district neonates referred for diagnostic audiology were excluded.

In total 11 606 babies received an initial test.

Of the infants tested, 810 (7%) had been admitted to the Whipps Cross or another special care baby unit.

The proportion of those enrolled who received an initial TEOAE test is illustrated longitudinally for the three years of the evaluation in fig 2.

Over the entire period only 81% of those

eligible

for entry into the screen was received an initial TEOAE test.

This attributable to a rise in the proportion tested over the initial nine months. Two substantial improvements occurred. The first was at three months when the number of hearing screeners was increased.

The second was at nine months, and involved several factors. The number of babies tested before discharge from the maternity unit was increased. This entailed more than within the

doubling

the

proportion

tested

maternity

unit during the first day of life. During the first nine months of 1992, only

18% of those receiving an initial screen were tested within the first

24 hours of life.

However, this rose to 37

5% over the

remaining

period.

The increase in those receiving the initial test was also assisted by the computerised identification of babies discharged before they were tested, and those not born at

Whipps

Cross.

These improvements were implemented by the end of

September

1992.

Thereafter the proportion of those enrolled who received the initial

TEOAE test rose to 94% and remained stable for the remaining period.

TEST CONDITIONS

The testing conditions are detailed in table

2.

Samples of just over

1000

sequential

tests undertaken on the

1994 were

maternity

unit in 1993 and analysed. The samples represented

-inWaltham Forest residents

--o--

Whipps Cross Hospital deliveries

-v-- Waltham Forest residents born outside district

Table 2 Testing conditions of initial TEOAE test undertaken in the maternity unit at Whipps Cross Hospital

Version of IL088

Sweep time (ms)

Sample size

Stimulus (dB

Mean (SD) peak)

5%

50% 95%

Stimulus stability (%)

Mean (SD)

5% 50% 95%

Noise reject level (dB)

Mean (SD)

5% 50% 95%

No responses averaged

Mean (SD)

5% 50% 95%

No responses rejected

Mean

(SD)

5% 50% 95%

Noise level (dB)

Mean (SD)

5%

50%

Test time

Mean

(SD)

5% 50%

95%

(mins)

95%

1993

3-92

12-5

1025

86 (4)

80 85 91

77

(25)

15 86 97

46 (2)

43 45 48

143 (69)

58 124 256

584 (588)

75 378

1721

35 (3)

31 35 40

3-0

(2-6)

0-7

2-1 8-0

1994

3-94

12-5

1010

77

85 (5)

85 91

74

(27)

9 83

97

44

48 (2)

47 50

154

(70)

59 139 256

540

(548)

65

357

1618

37

(3)

32 36 42

2-9

(2 3)

0-8 2-2 7-5 test conditions when the initial screen was being undertaken by different testers working to the same criteria and within the same testing environment.

AGE AT INITIAL TEOAE TEST

Of the

12 682

Whipps

Cross

Hospital

deliveries, 8750 (69%) were discharged home within 48 hours. This

early discharge governed

the age at which the initial test was

possible.

The age of the infants at the initial test is detailed in table 3.

Of the babies tested, 10 649 were born at Whipps

Cross, with an additional

957 infants being born elsewhere. For the total of

11 606 infants tested, the mean initial test age was 1 9 weeks.

Inevitably

the infants born elsewhere were tested after discharge from their

maternity

unit. Of the births at

Whipps

Cross, only

9133

(86%)

could be tested before they were

discharged

home. The mean test age of these infants was 61 hours. Those missed on the

maternity

unit were called back later to the

audiology department,

along with those born elsewhere. The mean age of all the infants called back to the

audiology department

for their first test was 7-4 weeks.

Of those 9133 tested before were cared for in the

special discharge,

care

635 baby unit.

Their mean test age was

2-7 weeks. The difference in the distribution of test age for all the infants, and for those requiring special care, is illustrated in

fig

3.

The exclusion of

100

_ m60

C a)

4

4

4

20 o

80

--o-=-

D _

-_

--0

3 6 9 12 15 18 21 24 27 30 33 36

Months

Figure 2 aggregated

PAroportion

receiving initial TEOAE test, quantity.

Table 3

Age of infants at initial test

No Mean tested age

Age range

Infants admitted to SCBU

Tested

Tested

Total before discharge after discharge

635 2-7 w 2-9 h-19-8 w

175 7 9 w 1-9 w-22 7 w

810 3-8 w

2-9 h-22-7 w

Infants not admitted to SCBU

Tested before discharge

Tested after discharge

Total

8498

2298

10796

32-7 w

7-4 w

1-0

1-0 h w

-2-2

-20-3 w

1-7w 1-0h-20-3w w

All infants tested

Tested prior to discharge

Tested after discharge

Total

9133

2473

11 606

61-4 h

1-0 h-19-8 w

7-4w 1-0 w-22 7 w

1-9 w 1-0h-22-7w

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F20 Watkin

(D

'

(D

.0

4500

(D

.s

c

4000

3500

3000a

2500

A z

2000

1500

LI Infants tested before

discharge

* Infants tested after discharge

1 2

Days

3 4 5 6 7 2 3

4

5 6

7

8 9 10 11 12 13 14+

Weeks

All infants tested

TEOAE RETEST

Of the

1393 referred because of bilateral failure at the initial test, 1202 (86%) received a

TEOAE retest.

The mean age at the retest was

7-7 weeks (range 0 5 to 40 weeks).

Of those retested,

999 passed in one or both ears.

However, 203

(1.75%

of those initially tested) failed the TEOAE screen on two occasions in both ears.

Of these

406 ears, 300 demonstrated no TEOAE response, and of the remaining 106, 44 could not be adequately tested, and

62 were borderline.

Those with borderline responses or an inadequate test required an ABR along with those where there was clearly no response.

Thus 337 infants

(2.9%

of the initial cohort tested) required a diagnostic ABR because they had failed the TEOAE in both ears.

Of the

887 unilateral failures who were retested by

TEOAE recording, 108 (0-9% of the initial cohort tested) failed the test again in one ear.

In total 91 infants underwent

ABR testing because they had failed the TEOAE unilaterally.

200 in

175

(D

.x

150

, 125

100

_

B

75

LII Infants tested before

discharge

* Infants tested after discharge

ABR EXAMINATION

Of the 337 infants referred for

ABR examination because of bilateral TEOAE

failure,

290

(86%) were tested.

An additional

91 infants were was age tested because of failure in one ear.

ABR thus undertaken on 381 infants. The mean of the

ABR was 12-8 weeks, with a range from

1 to

33 weeks. Two of the

ABR examinations were only completed in one ear.

The

ABR thresholds measured from the better and worse ears are detailed in fig

6.

E

50

Figure

3

1 2 3 4 5 6 7 2 3 4 5 6 7 8 9

10 11 12 13 14+

Days Weeks

Infants admitted to the special care baby unit

Distibution of initial test age.

those

requiring special

care reduced age for those tested on the before discharge to 32-7 hours.

the

maternity

mean unit

COVERAGE OF THE SCREEN

The coverage of the screen for the different sources was of enrolment and for the overall cohort computed from the data presented in

fig

4.

The number receiving the initial TEOAE test was reduced by the number of bilateral failures not nents completing the retest and ABR compoof the screen.

The computed data for coverage are presented in table 4.

RESULTS OF

THE

INITIAL TEOAE TEST

The number detailed in

fig failing

4 the test in both for the different ears sources is of enrolment to the screen.

The combined data are shown in

fig

5.

Of the cohort

tested,

1527

(13%)

failed the initial test in both ears.

Of these

3054 ears, 2336

(10%

of those

initially tested)

had no

TEOAE response

according

to the scoring criteria used.

An additional

261 ears the

(1%)

were not

adequately

tested because

baby

would not

settle,

and

457

(2%)

were borderline responses.

In

addition,

2398

(21%)

of the cohort tested failed in one ear. Of the bilateral failures, 134 (1 15% of those initially tested) were referred immediately for ABR.

The other 1393 (12% of those initially tested) were referred for a TEOAE retest. Of the unilateral failures, 887 parents elected for a retest

(7.5%/ of those initially tested).

YIELD

OBTAINED FROM THE SCREEN

The yield in terms of ABR threshold is detailed in table 5.

The aim of the screen was to identify those with a moderate or worse

degree

of bilateral permanent

hearing impairment.

Most of those with a

40 dBnHL or worse

ABR threshold had middle ear effusions without an underlying permanent hearing impairment.

After

diagnostic audiological

assessment 23 were found to have a permanent hearing

impairment targeted by

the screen and

requiring long

term

audiological

rehabilitation.

This was a

yield

of

2 per 1000 neonates who had received the initial test.

COST

The cost of the screen is detailed in table 6.

The screen required a testing room on the unit. Within this maternity facility around 3500 tests were

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Neonatal otoacoustic emission screening and the identification of deafness

Total No requiring test

14,353 (10,750)

Not born at Whipps Cross

1671 (1252)

Born at Whipps Cross

12,682

(9498)

F21

Non-district residents for

Initial OAE

53 (53)

Tested

34(34)

District residents for

Initial OAE

1618 (1199)

Tested

923 (915)

District residents for

Initial OAE

9850

(7400)

Tested

8303

(7120)

Non-district residents for

Initial OAE

2832

(2098)

Tested

2346

(2011) for

ABR

4 (4)

2 ear fail

8 (8) for OAE retest

4

(4) for ABR

31

(30)

2 ear fail

74(73)

2 ear fail

1123(1014)

2 ear fail

322(295) for OAE retest

43 (43) for ABR

84

(76) for

OAE retest

1039 (938) for for OAE

ABR retest

15

(15) 307 (280)

Tested

3 (3)

2 ear fail

0

(0)

Tested

27 (27)

2 ear fail

10

(10)

Tested

907 (820)

2 ear fail

141

(134)

Tested

265 (239)

2 ear fail

52

(50)

ABR tested

4

(4)

ABR tested

0

(0)

ABR tested

27(26)

ABR tested

7

(7)

ABR tested

72(71)

ABR tested

123(116)

ABR tested

14

(14)

Figure 4 Results of screen from

1

January

1992 to

31

December 1994; numbers after

1

October in parentheses.

ABR tested

43(42) undertaken annually by an assistant technical officer employed for a single session every day including weekends. An average of 10 neonates were tested per 3-5 hour session, with parental discussion and the required administration.

Cover for holidays was essential.

An additional 2500 appointments were made in the audiology department for a senior assistant technical officer to test those missed on the maternity unit, those born elsewhere, and the initial TEOAE failures. The number of appointments included a

20%

non-show rate.

The rate of testing was also 10 babies per 3-5 hour session. The senior officer was employed full time. She had additional duties, including data entry, administration, and the responsibility for screening those babies admitted to the special care baby unit. Holiday cover has been included in the costing, but weekend cover was not required.

She was assisted in the administration by a 0 5 whole time equivalent clerk.

A senior audiological scientist was employed in the audiology department to undertake the

ABR examinations. This required two sessions per week. The subsequent diagnostic audiological assessments have not been included in the cost analysis. Staff costs were calculated as being midway on the salary scale including additional costs of National Insurance,

Superannuation, and London Weighting.

Equipment costs have been amortised over five years, with the annual cost of disposables including TEOAE probes, ABR electrodes, and stationery, etc, included.

The annual cost of screening 4500 neonates and of testing the screen failures with ABR was

£44,200, or

£9.80

per baby tested. With a yield of 2/1 000 with a bilateral loss of moderate or worse degree, the cost per

hearing impaired

child usefully detected was £4900.

Discussion

The early identification of congenital deafness has been the frustrated aim of preventive child health services for many years. Yet quality

F22

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Watkin

Referred for

TEOAE retest

1393

TEOAE retest received

1202

Failed initial screen in both ears

1527

Failed retest TEOAE in both ears

203

Total No rceiving initial

TEOAE screen

11,606

Referred for ABR without TEOAE retest

134

Referred for ABR

203

Figure 5 Number of infants failing

TEOAE in both ears.

initial and retest standards have now been set, requiring the detection of

40% of bilateral congenital deafness within the first six months of

Unfortunately,

deafness presents

life.'9

subtly20 and the only realistic way of meeting this target is by neonatal screening. Targeted neonatal screens may identify two thirds of the congenitally ably

deaf,2'

but the yield may be consider-

lower.6

At risk neonatal screens would probably have to function with very high sensitivity to meet the quality standards.

The technology is now available for screening all neonates, and the temptation to implement such programmes is difficult to resist.

This report details one of the first universal TEOAE

screening

programmes to be implemented in the United Kingdom. The process to and outcome evaluation has been used

investigate

some of the concerns

expressed

about practicability and

cost.5

6

Can high a coverage be achieved at reasonable cost?

Can balance be struck between test sensitivity and

specificity

so that a worthwhile

yield

is achieved without

inundating already

stretched

audiology departments

with concerned parents and normally hearing neonates?

Experience

with the distraction test has shown that the success or demise of a universal screen is

intrinsically

linked to the coverage.22

Poor coverage inevitably leads to a low yield, irrespective of the sensitivity of the test being used. The worth of the screen for a district depends on

achieving

high coverage. Sur-

prisingly,

it has not been

possible

to ascertain what coverage has been achieved from other reports of universal neonatal applied in this

country'0 hearing

screens or in the USA.23

The very attraction of implementation within the maternity unit is the presence of a captive population and the possibility of effectively testing a large proportion of those targeted for the screen. However, is this really practicable in a maternity unit where over two thirds of the babies are discharged within the first two days? District coverage also depends on the ability to undertake an initial test on those infants born elsewhere, and on retesting those failing the initial test.

These different components of the screen were examined in

Waltham Forest.

Difficulties were encountered over the first few months

following

the introduction of the screen.

However, thereafter the proportion of all those eligible for screening who received the first test rose to a stable level of 94%.

Over

96% of those born within the district maternity unit received an initial test, with

86% being tested before discharge home. This required the employment of weekend staff, and also holiday cover.

The continuity of the screen during periods of absenteeism was facilitated by the deployment of two other assistant technical officers familiar with the programme but

normally

employed elsewhere within the district.

The proportion of those residents not born in the district maternity unit, who received an initial test, remained disappointingly low at

76%. Improvement may have been

possible

by TEOAE testing in community clinics.

However, this would have

considerably

increased the programme cost, and because over

85% of

district births occurred in the district hospital, the difficulties of born elsewhere only

enrolling marginally

those reduced the overall district coverage.

The proportion of those

TEOAE retest and ABR remained at

86%.

This has been the coverage of other subsequent hearing screens

receiving

a required

within

the district.14

Improving this required imaginative measures not yet achieved.

Retest TEOAE failures should clearly result in an immediate ABR test but

this

has proved

logistically

difficult.

However, despite problems

the these

reported partly unresolved screen methodology has achieved a stable district coverage of 91-5% since October

1992.

* ABR threshold in better ear

150

125

,,100

-

A

138

94

E

75

25

52

Z 50 -40

-26

0

1

21

3 11

13

10 20 30 40 50 60 70 80 90 100>100 dBnHL

150

-

| ABR threshold in worse ear

5

125-

0

100

115

7

6721

25 0

0O

10 20

30)

40 50

60O

70 80 90 100>100 dBnHL

Figure 6 ABR thresholds in better and worse ears.

Downloaded from http://fn.bmj.com/ on September 29, 2017 - Published by group.bmj.com

Neonatal otoacoustic emission screening and the identification of deafness

F23

Table 4 Coverage of the screen for the enrolment different sources of

Coverage

1/1/92 to 1/1 0/92 to

31/12/94 31/12/94

Non-district residents not born at

Whipps Cross

District residents not born at

62-3% 62-3%

Whipps Cross 55-6% 74-4%

District residents born at Whipps Cross 82-6% 94*3%

Non-district residents

Whipps Cross born at

81-0% 93-5%

All births at

All

All

Whipps Cross births of district residents enrolled for screen

82-3%

78-8%

79-2%

94-1%

91-5%

91-8%

Haggard's

caution6

about universal screens swamping the available assessment facilities is well founded. The screen specificity was lower than has been reported elsewhere. The largest

TEOAE screen has been the Rhode Island

Hearing Assessment

Project.23

This was initiated some two years before the Whipps

Cross programme and although the two stage procedure was essentially similar, the TEOAE scoring criteria were less stringent in the

American programme.

From the first cohort of

1850 Rhode Island births, the failure rate of the initial test was

27%.

However, recategorisation of borderlines reduced this to

15%.

The age of initial testing was of necessity lower in the Whipps Cross programme. It has been established by other

studies7-9

that testing within the first two days results in high failure rates.

However, an acceptable level of coverage was only obtained by testing the well babies in the district maternity unit at a mean age of

33 hours.

This inevitably affected the test specificity.

The one and two ear failure rate of the initial test totalled

34%.

Only

2% out of the

13% who failed in both ears, and 5% of the 21% failing unilaterally, were borderline responses.

If these were considered to be screen passes, then the total initial failure rate would have fallen to

27%. This was considerably higher than the

15% reported from Rhode Island. The aim of the

Whipps

Cross programme,

however,

was the identification of bilateral losses. The policy of retesting all 13% who failed bilaterally, but only reappointing unilaterals as required, kept the programme

manageable.

In part, the poor specificity seen in the current programme is attributable to the drive for increased testing before discharge. The advantages of

having

a

captive population

within the

maternity

unit were thus

partly

negated. However, the number of neonates

discharged

from the

maternity

unit within the first two days was some

20% higher than the national average. Such low specificity may

Table S Yield obtained from the TEOAE screen

ABR threshold in better ear

340OdBnHL

250 dBnHL

260 dBnHL

270 dBnHL

280 dBnHL

290 dBnHL

2100 dBnHL

Number

122

70

30

9

5

6

4

Yield/1000 screened

10-5

6-0

2-6

0-8

0 5

0 4

0 3 therefore not be experienced by other districts.

The Whipps Cross programme could also have been made more specific by making the criteria less stringent and by the effective use of response filtering, and the same day retesting of babies failing the initial test.

Such measures are being investigated, but increasing specificity must eventually result in reduced sensitivity. Because sensitivity measures require long term follow up of the entire cohort, such changes are being implemented with caution.

Measurement of the sensitivity of the test requires complete ascertainment of all those within the cohort with a permanent congenital hearing impairment. This will require at least five years of follow up of the cohort, and without a larger multicentre trial confidence limits of these measures will be wide. The effect on the age of detection of permanent hearing impairments within the district will also require long term follow up.

However, yield can be used as a short term surrogate for evaluating test sensitivity. The yield of infants identified with a bilateral permanent was hearing loss of moderate or worse degree

2/1000. There was a higher proportion of infants with a moderate loss, in keeping with the expected distribution of hearing threshold found in congenital deafness.

Although

specificities have been

higher

than that

experienced

within the present programme, this expected distribution has not been reported from behavioural universal neonatal

Auditory Response

screening

Cradle.10

using the

Following the ABR examination, 10-5/1000 were identified from the present cohort with a

40 dB or worse

hearing

loss in the better ear.

Although this seems to be a high yield, most had middle ear

effusions,

and the value of identifying such temporary conductive losses at this age is

currently

unclear.

Undoubtedly, this group also contains some with mild permanent the losses. This will become clearer with

long

term follow up of the cohort. The yield of those with a unilateral loss was also omitted from the present were not targeted

by

the

evaluation,

screen.

as they

The yield shows that the screen was reasonably sensitively

implemented.

The prevalence within the district of congenital deafness of moderate or worse

degree

has

averaged

3/1000 since

1973.14

The

yield

from the three year cohort

receiving

the neonatal screen is

slightly

lower. It is extremely unlikely that the programme

sensitivity

could have been 100% because of the

inability

to retest with ABR all those

failing

the TEOAE tests.

Table 6 Annual cost of TEOAE screening programme

1

Equipment amortised over

3

IL088 systems

1 ABR

Machine

Computer+software

Syears

Annual cost of disposables

Stationery, probes, electrodes, etc

Staff

0-2

WTlE1 audiological scientist

0-8

WTE assistant technical officer

1-1 W'TE senior assistant technical officer

0-5

WTE clerical assistant

Total: cost/year

C4560

£1900

£220

£3 100

£C6200

£g8424

£14

179

£5635

£644

218

F24

Downloaded from http://fn.bmj.com/ on September 29, 2017 - Published by group.bmj.com

Watkin

A stringent assessment of cost is required in any programme evaluation.

The total cost of the reported neonatal programme at just under

£45

000 a year was similar to the district's pricing of the infant distraction screen. The cost of each neonatal test was under £10.

Clearly this low cost reflected the professional grading of the hearing screeners.

Because the

TEOAE test is essentially repetitive and readily learnt over a few weeks, this component of the screen was implemented using assistant technical officers without previous audiological training.

Although other universal screens have recommended the employment of nursery nurses,10 the performance of the former has been regularly monitored, and no significant problems have been encountered. However, the cost of the screen also included the employment of an audiologist to undertake threshold ABR examinations on the TEOAE failures.

Such inclusion is at odds with the concept of a screen.

The cost of the audiologist made up almost one quarter of the overall cost of the testers, and the use of automated

ABR recording by the assistant technical officers is being investigated.

In 1990 the notional cost per deaf child identified by targeted neonatal screening was considered to be around

£4000.6

When inflation is taken into account, the cost of

identify-

ing a deaf child by the reported universal screen was scarcely much more.

In Waltham Forest the infant distraction test has been retained until the sensitivity of the neonatal screen becomes clear. The incremental yield from this later screen is under evaluation. If this later screen can be withdrawn the saving will almost entirely offset the cost of the neonatal screen.

The screen detailed has been of undoubted worth to the district in terms of the

yield

of infants identified with a permanent hearing loss.

Although such early identification does not necessarily allow for early and successful habilitation, the wider application of this universal screen nationwide requires consideration.

Currently, large multicentre trials of

TEOAE test sensitivity are being undertaken both in the USA and Europe. The current data have been included in the European cohort, and the district cohort is subject to

long

term follow up.

The need to plan for the introduction of such a screen in other districts in the

United

Kingdom

is not

universally

acknowledged.

A selective neonatal screen of those with risk

factors,

sensitively applied, may iden-

tify

most of those with congenital deafness.

However, this was not the case in Waltham

Forest, and similar districts should consider the

opportunity

afforded

by

the

recently developed

technology for the detection of

otoacoustic emissions.

The logistics of implementing such a screen are challenging.

for a TEOAE

Although the average test time recording undertaken on a neonate on the maternity unit was three minutes, only between three and four babies could be tested each hour. Most of the time was taken up with transporting the baby to the test site, and discussions with the mother. With a modal birth rate of

13 per day it was not feasible to achieve efficiently complete testing before discharge from the maternity unit. The number of new births per day ranged from four to 25.

This inevitably resulted in days when complete coverage was not possible for the single screener employed to undertake initial tests for one 3-5 hour session each day. On almost 20% of days more than 16 babies were born.

However, for 10% of days fewer than eight neonates required screening.

Simply to increase the screening time to ensure a higher proportion tested before discharge would have been effective but not efficient.

Instead the present methodology elected to recall a minority. The presence of a facility to test those missed on the

maternity

unit, and also those district babies born elsewhere was thus essential to achieve the coverage of over

90%. Districts with different birth rates require an individual logistical assessment, but the numbers born in Waltham Forest are not atypical, and similar problems can be anticipated elsewhere.

The maternity unit reported is atypical, however, in that almost 70% of the babies were discharged home within 48 hours.

This resulted in a higher than expected failure rate from the initial TEOAE test. A two stage

TEOAE test was therefore implemented. If initial testing can be delayed until after the first day or two of life the failure rate will be

reduced.7-9

However, in the United Kingdom just over

50%

of babies are discharged within the first two days, and thus in many

maternity

units similarly low specificity for the initial test will apply.

A two stage test is effective in reducing the number of babies requiring an ABR examination.

Even with a two stage TEOAE screen, however, around 3% of the cohort

required

an

ABR examination. Although it is anticipated that less

stringent

TEOAE

scoring

criteria can further

improve

test

specificity,

the local

provi-

sion of a neonatal ABR service is considered an essential precursor to

implementing

a

TEOAE screen.

Although the reported screen is now a valued and effective district service, it is still evolving some three years after initial implementation. It is not anticipated that the screen can have been

absolutely

sensitive to all

degrees

of congenital

hearing impairment,

and it is considered that methods of identifying progressive and acquired hearing losses later in childhood are still

required.

In districts where an adequate yield of infants with congenital hearing loss cannot be achieved

by

selective at risk neonatal screens, it is feasible to implement a universal neonatal

TEOAE screen.

The cost is not

prohibitive,

and the number of infants identified

by

the

Whipps

Cross programme is testament to the sensitivity of the screen. The specificity of the screen was low because the pass/fail criteria were set to ensure a high level of test sensitivity.

This was considered to be necessary with the implementation of a new programme.

The achievement of high coverage also entailed the testing of most neonates within the

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Neonatal otoacoustic emission screening and the identification of deafness F25 maternity unit before they were 2 days old.

This further reduced the test specificity.

It is anticipated that this will be a problem common to many districts in the United Kingdom currently considering the implementation of such a universal neonatal screens. Even so ure rate has not rendered the the failprogramme unacceptable.

It is predicted that the criteria can be relaxed and this is currently under investigation. If the specificity can be improved without loss of sensitivity, then universal neonatal TEOAE screening becomes an attractive proposition, even in maternity units with high early discharge rates.

I gratefully acknowledge the continuing advice, assistance and encouragement received from Professor D Kemp of the

Institute of Laryngology and Otology, London.

1 National Institutes of Health. Early identification of impairment in infants and young children.

Maryland: NIH Consensus Statement 1993.

hearing

Bethesda,

1993;

11:

1-24.

2 Stevens JC, Webb HD, Hutchinson J, Connell J, Smith MF,

Buffin

JT.

Click evoked otoacoustic emissions compared with brain stem electric response. Arch Dis Child 1989; 64:

1105-11.

3 Kemp DT.

Stimulated acoustic emissions within the human auditory system.

J Acoust Soc Am 1978; 64: 1386-91.

4 Bray P, Kemp DT. An advanced cochlear echo suitable for infant screening. Br

J

Audiol technique

1987;

21:

191-204.

5 Bess FH, Paradise

JL.

Universal hearing screening for infant

6 hearing impairment: not simple, not risk free, not necessarily beneficial, and not presently justified. Paediatrics

1994; 93: 330-4.

Haggard art(s). Arch Dis Child

7

Vohr BR,

M.

Hearing screening

White KR,

1990; in children

65: 1193-8.

Maxon AB,

state

Johnson MJ.

of the

Factors affecting the interpretation of transient evoked otoacoustic emission results in neonatal hearing screening.

Semin Hear 1993; 14: 57-72.

8 Salomon G, Groth J, Anthonisen B.

Preliminary results and considerations in hearing screening of newborns based on otoacoustic emissions. Br J Audiol 1993; 27:

139-41.

9 Thomton ARD, Kimm L, Kennedy CR, Cafarelli-Dees D.

External and middle ear factors affecting evoked otoacoustic emissions in neonates. Br Jf Audiol 1993; 27:

319-27.

10 Tucker SM, Bhattacharya J. Screening hearing impairment in the newborn using the auditory response cradle. Arch

Dis Child 1992; 67: 911-19.

11

Kennedy CR, Kimm L, Dees DC, Evans PIP, Hunter M,

Lenton S, et al. Otoacoustic elisions and auditory brainstem responses in the newborn. Arch Dis Child 1991; 66:

1124-9.

12

Watkin PM, Beckman A, Baldwin M. The views of parents of hearing impaired children on the need for neonatal screening. BrJAudiol 1995; 29: 259-62.

13 Watkin PM, Baldwin M, McEnery G.

Neonatal at risk screening and the identification of deafness. Arch Dis

Child 1991; 66: 1130-5.

14 Watkin PM. The age of identification of childhood deafness

improvements since the 1970's.

303-12.

15 Kemp DT, Ryan S, Bray P. A guide to the effective use of otoacoustic emissions. Ear Hear 1990; 11: 93-105.

16 Kemp D, Ryan

Public Health 1991; 105:

S. The use of transient evoked otoacoustic emissions in neonatal hearing screening programs.

Semin

17

Hear 1993; 14: 30-44.

Baldwin M, Watkin PM. The clinical application of otoacoustic emissions in

J

Laryngol Otol

18 Richardson MP,

1992; paediatric

106: 301-6.

Williamson TJ, audiological

Lenton

SW, assessment.

Tarlow

MJ,

Rudd PT. Otoacoustic emissions as a screening test for hearing impairment in children. Arch Dis Child 1995; 72:

294-7.

19 The National

Deaf Children's Society. Quality standards in paediatric audiology.

Guidelines for the early identification of hearing impairment. London: NDCS,

1994.

20 Watkin PM, Baldwin M, Laoide S. Parental suspicion and the identification of hearing impairment.

Arch Dis Child

1990; 65: 846-50.

21

Sancho J, Hughes E, Davis A, Haggard M.

Epidemiological basis for screening hearing.

In: McCormick B, ed.

Paediatric audiology, 0-5 years.

London: Taylor and

Francis, 1988: 221-46.

22

Brown J, Watson E, Alberman E.

Screening infants for hearing loss. Arch Dis Child 1989; 64: 1488-95.

23 White ment

KR, Behrens TR. The Rhode Island hearing assessproject, implications for universal newborn hearing screening.

Semin Hear 1993; 14: 1-122.

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Neonatal otoacoustic emission screening and the identification of deafness.

P. M. Watkin

Arch Dis Child Fetal Neonatal Ed

1996 74: F16-F25 doi: 10.1136/fn.74.1.F16

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