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Controlling the quality of universal neonatal hearing screens
Public Health (1999) 113, 171±176 ß R.I.P.H.H. 1999 http://www.stockton-press.co.uk/ph
Controlling the quality of universal neonatal hearing screens PM Watkin1* 1
Audiology Department, Whipps Cross Hospital, Whipps Cross Road, Leytonstone, London, E11 1NR, UK The Health Technology Assessment Programme has recently reviewed the role of neonatal screening in the detection of congenital hearing impairment. The review recommends that the health visitors distraction screen, currently implemented in the second half of infancy, should be replaced by a national programme based around universal neonatal hearing screening. Such a programme has been implemented as a routine and established service in Whipps Cross Hospital in the East London district of Waltham Forest. This programme has reinforced the need to routinely monitor the screen processes and outcomes. The Whipps Cross audit undertaken over a 2 y period from January 1996 is detailed, as are the targets employed for evaluating the processes. The monitoring ¯agged up implementation problems, and allowed remedial intervention. Monitoring should be built into all the universal neonatal hearing programmes currently being planned in the UK. Keywords: hearing testing; universal neonatal screening; quality monitoring
Introduction For half a century the identi®cation of congenital deafness has been widely accepted as an appropriate aim of public health services in the UK. The 1944 Education Act, and subsequently Section 22 of the 1946 National Health Service Act, provided the impetus for identifying hearing impaired children from birth onwards, but this has remained an elusive goal. By 1952 the distraction test1 was being used by health visitors to screen the hearing of babies during the latter half of infancy.2,3 Widespread implementation followed, but questions about the effectiveness of the Health Visitors Distraction Test (HVDT) were being increasingly voiced.4 ± 7 Even with a sensitive HVDT in place, consistent habilitation for many of those with a congenital hearing impairment has been delayed until school entry and most clinicians and parents consider this to be too late.8 Neonatal hearing screening has therefore reached the agenda. In 1993 the American National Institutes of Health recommended the hearing screening of all neonates, with the aim of introducing habilitation by six months.9 In the UK a recent NHS Health Technology Assessment report entitled `A critical review of the role of neonatal screening in the detection of congenital hearing impairment',10 also recommended universal neonatal hearing screening. This view had been pre-empted by some districts. By 1996, 23 out of 128 districts in England and Wales, were already hoping to implement a universal neonatal screen (UNS). At Whipps Cross Hospital such a screen has been implemented as a routine service since 1992.11,12 In the UK, much has been already been learnt about the trials and tribulations of universal infant hearing screens, and such lessons should not be lost. Importantly, the HVDT screen was not routinely monitored. It therefore took over 25 y of clinical experience, some focused evaluations, and the persistent questioning of the national parents organisation, for its effectiveness to be seriously doubted. However the climate has changed and audit is now routinised into clinical practice. From the outset, on-going monitoring has *Correspondence: Dr PM Watkin, Audiology Department, Whipps Cross Hospital, Whipps Cross Road, Leytonstone, London, E11 1NR, UK. Accepted 28 January 1999
been considered an essential component of the Whipps Cross UNS programme, and the methods employed in this quality control are presented. Universal neonatal hearing screening methods Several testing methods are currently being employed to screen neonatal hearing. The Auditory Response Cradle (ARC) is a microprocessor controlled device which tests the auditory behaviour of neonates.13 It has been used since the early 1980s to screen the neonatal population of a single district in the UK.14 The Auditory Brainstem Response (ABR) has become an established electrophysiological technique for auditory threshold measurement, but it is time consuming, and traditionally this has limited its use to selectively screening a small percentage of the birth cohort at risk of deafness. Automated ABR (AABR) waveform detection has now been developed for screening. Results are more rapidly obtained, facilitating AABR screening of the newborn cohort. This technique is being employed in several American states.15 However it was the description of Otoacoustic emissions at the Institute of Laryngology and Otology, London,16 and the commercial availability of simple recording equipment, that resulted in the resurgence of clinical interest in UNS.17 Otoacoustic emissions are very quiet sounds emitted from the normal cochlea. As long as there is no blockage in the middle or external ear, they can be recorded by a microphone in the ear canal. The simplest way of evoking them is with a transient stimulus such as a click delivered by a miniature speaker sited alongside a recording microphone in an ear canal probe. The recording of transient evoked otoacoustic emissions (TEOAEs) tests the auditory system to the level of the cochlea. However, absence of an emission does not give any information about the degree of impairment and neonates failing a TEOAE screen, require further testing by ABR. The combination of TEOAE testing followed by ABR was recommended by the NIH consensus statement. Although the critical review reported that a combination of TEOAE and ABR is likely to be the optimal method for UNS, recommendation of a speci®c screening system was
172
Quality of neo-natal hearing screens PM Watkin
avoided. In fact the authors considered that given high quality implementation, most combinations of tests could be made effective. In fact there is some commonality in the neonatal screening methods. Importantly, they can all be automated Ð facilitating the undertaking of the screen by less skilled personnel. This is a screening ideal18 which has never been achieved with the HVDT. However when programmes are undertaken by less skilled personnel, issues of routine quality control assume heightened importance. The Whipps Cross screening programme The Whipps Cross programme combines two stage TEOAE testing, followed by threshold ABR measurement for TEOAE failures. It aims at identifying those infants with a bilateral, congenital deafness of moderate degree or worse in the better ear. Although the programme employs only one of several possible test combinations, it mirrors the programme methodology of the HVDT screen, and has proven sustainable and effective for over 5 y. Such a programme has been used in various European centres, and is likely to be further employed in the UK. The constituent processes of the screen are detailed in Figure 1. An initial TEOAE test is undertaken whenever possible before discharge from the Whipps Cross maternity unit. Around 70% of the neonates are discharged within the ®rst 48 h, and unfortunately TEOAE recording at this age may be prevented by the presence of vernix and debris in the ear canal. The optimal test age is after the second day. The programme has therefore built in the further maternity testing of those who failed when initially tested below the optimal test age. These tests (or set of tests for an individual child), are collectively described as the initial TEOAE tests undertaken by the time of maternity discharge. Those missed in maternity and those born out of district or at home are identi®ed at four weeks of age from a register of births recorded on the Regional Interactive Child Health Computerised System (RICHS). They are appointed for their initial TEOAE test in the hospital audiology department, with entry to the screen being offered up to three months of age. All bilateral fails at the initial TEOAE tests are appointed for a TEOAE retest in the audiology department. In line with the aims of the screen, those failing the screen in one ear only are retested on parental request. Bilateral failure at the TEOAE retest prompts an obligatory diagnostic ABR undertaken by a senior audiologist. This test de®nes the degree of hearing impairment. The ABR test is also offered to unilateral failures on parental request, and for other cases of parental anxiety where early diagnosis is required, and also where there is a potential auditory neuropathy. When the ABR threshold is > 40 dB nHL in the better ear, follow up is undertaken within the paediatric audiology department. Here further audiological investigations are undertaken to clarify the type of hearing loss. For those con®rmed with a permanent hearing impairment moderate or worse in degree, the need for habilitation is discussed with the family. The infant is subsequently seen in the combined clinic with the teacher of the deaf, and an intervention programme and home visiting is introduced. Monitoring the screen It has been recommended that outcomes for local cohorts aggregated, for instance, over a 2 y time span, are the most
Figure 1 The Whipps Cross universal neonatal screen programme model.
feasible and accessible measure for monitoring a hearing screening system.19,20 Monitoring the processes involved in the screen has less face validity than measuring outcomes, and may be construed as simple number counting. However if a screening test is of acceptable sensitivity, then the effectiveness of the screen is dependent upon the correct implementation of the processes. Such issues also affect the test failure rate and the screen acceptability. When the condition targeted for detection is of low prevalence a large majority of those failing the screening test will be false positives Ð and these stress the system. A system unacceptably stressed inevitably fails and monitoring correct screen implementation highlights problems before outcomes have been affected over a prolonged period. Such processes need to be measured against standards of acceptable practice. The Whipps Cross programme was evaluated for an initial 3 y cohort of 14 353 infants.11,12 The screen gave a yield of 1.25=1000 with a targeted deafness. The results were used to set standards for subsequent monitoring. The results of the monitoring over a 2 y period for 1996 and 1997 are presented. Throughout the period, the results were fed back to the screeners through regular audit meetings. Monitoring screen processes The processes requiring monitoring, and the performance targets employed in the Whipps Cross audit are detailed in
Quality of neo-natal hearing screens PM Watkin
Table 1 The processes monitored and the targets set Cohort size and coverage (i) All infants eligible for enrolment to be identi®ed and categorised by place of birth and residence (ii) > 95% of each subcohort to receive initial TEOAE test (iii) No bilateral TEOAE fails to be lost to follow up with 100% receiving a further test (iv) > 95% coverage achieved for overall cohort TEOAE testing on maternity (i) > 50% of TEOAE fails on maternity to receive a further test before discharge (ii) > 85% of Whipps Cross births receiving the TEOAE screen to be tested before discharge The results of the TEOAE testing (i) < 10% of initial TEOAE tests to fail bilaterally whether receiving the initial test in maternity or after discharge (ii) < 1% of TEOAE retests to fail bilaterally The ABR tests (i) Diagnostic ABRs to be undertaken on all bilateral TEOAE retest failures, and whenever threshold or neurological testing is requested by parents or other professionals (ii) All those with > 40 dB nHL threshold in the better hearing ear to be referred for further diagnostic assessment within the paediatric audiology department.
Table 1. Achievable targets have been set. Test quality and the accuracy of screener interpretation of pass=fail criteria is checked for a > 10% sample of hardcopied emission recordings on a weekly basis by a senior audiologist. The screen processes are audited for a monthly aggregated cohort of rising six month olds. This time lag allows for completion of the processes for those late screen entrants failing the TEOAE tests and requiring ABR. Monitoring cohort size and coverage Four sub-cohorts are included in the overall screen, and the percentage of infants receiving the initial TEOAE test is audited for each. Coverage is measured as the percentage of all the babies eligible for enrolment who receive the screen to completion. Because of the screen aims, those failing the TEOAE test(s) bilaterally and not attending for the retest in the audiology department, or for the ABR are considered to have reduced the coverage. During the 2 y of 1996 and 1997, the total cohort numbered 9680. The largest of the four sub-cohorts consisted of the 6522 Waltham Forest residents who were born at Whipps Cross. An additional sub-cohort of 1977 Whipps Cross births were not district residents, with 1124 Waltham Forest residents being born either at home or out of district. Fifty-seven babies were neither district residents nor born in Whipps Cross. They were usually staying with relatives, or were resident on the district borders. The percentage of the sub-cohorts receiving the initial TEOAE test is detailed in Figure 2. The small non-district, non-Whipps Cross cohort was not graphically presented, as enumeration implied that the tests had been undertaken. Over the audit period a monthly mean of 97.4% district residents and 96.6% non-district residents born at Whipps Cross received the initial TEOAE test. The > 95% target was always achieved for the former subcohort and achieved two thirds of the time for the latter. However, despite increased publicity and professional awareness training, the target was never achieved for Waltham Forest residents who were not born at Whipps Cross. Up to March 1997, a monthly average of 71% of this sub-cohort had received the test. After this the universal HVDT was dropped in the district, and for the remaining nine months of the audit period, an average of 83% received the initial test with the target still not being achieved in any month. The reasons were investigated and attributed to two factors. A minority of parents were
Figure 2 The percentage of the cohorts receiving the initial TEOAE test and the overall coverage.
reluctant to attend Whipps Cross, when they had elected to have their babies born elsewhere. There was also incomplete referral of babies moving into the district up to three months of age. The inadequate enrolment of this sub-cohort reduced the overall coverage. The bilateral TEOAE test failures not completing the programme also reduced the coverage, but in fact this number was small (mean of four per month), with a monthly average of 91.8% of those failing a TEOAE test bilaterally, receiving a further test. Inadequate enrolment, rather than large losses to follow up, was the main factor resulting in a disappointing, monthly average coverage of 93.7%. Only 3 of the 24 monthly cohorts achieved the coverage standard of > 95%. Further measures to improve enrolment of district residents not born in Whipps Cross, are necessary for this standard to be consistently achieved. Such strategies are being planned. Monitoring TEOAE testing on maternity Auditing the percentage of Whipps Cross births who receive their initial TEOAE test before discharge, ensures adequacy of screener input to maternity. A target of > 85%
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was set from the 3 y evaluation. This was achieved for one third of the months audited in 1996 and 1997. A monthly average of 83.3% of the babies born at Whipps Cross were tested before discharge. An enthusiastic high of 90.7% was achieved early in 1996, with a low of 70.9% recorded for the holiday month of August 1966. Action was taken to support maternity testing over the holiday period the following year. There were also ¯uctuations in the further maternity testing of those failing the TEOAE test when initially tested at a sub-optimal age. The target set from the 3 y evaluation was that 50% of such initial test failures should receive a further TEOAE test by the time of maternity discharge. This target was only achieved for one third of the months audited. Monitoring the crude failure rates of the TEOAE tests The failure rates of the initial TEOAE tests undertaken in maternity by the time of discharge, and in the audiology department, are monitored. The results of the initial TEOAE tests undertaken by the time of maternity discharge, combined with the results of the initial TEOAE tests undertaken after discharge, are detailed in Figure 3. A target of < 10% for bilateral failure at the initial TEOAE test was set from the 3 y evaluation. In line with the aims of the screen a target for unilateral TEOAE failure was not set, although it is still monitored. The average monthly bilateral failure rate was 10.5% with the target of < 10% being achieved for half of the audit months. In addition to those failing bilaterally, a monthly average of 13.9% failed the initial TEOAE test unilaterally. The crude failure rate of the initial tests undertaken in maternity and after discharge, were separately monitored. As expected, the failure rate for the initial TEOAE tests after discharge was relatively low, and in all but one month the target was achieved for both unilateral and bilateral failure. Higher failure rates were experienced when the initial TEOAE tests were undertaken in maternity. From March 1996 for the rest of that year, there was an average monthly maternity bilateral failure rate of 15.7%. Staf®ng changes early in 1997 reduced this and thereafter the bilateral rate once again achieved the target.
Figure 3 The crude failure ratio of the initial TEOAE tests.
The results of the TEOAE re-tests are detailed in Figure 4. The average monthly bilateral TEOAE retest failure rate was 0.9%, with an additional 1.5% failing unilaterally. The target of < 1% failing the retest bilaterally was achieved in exactly half of the months. ABR Tests These tests were monitored each month. However targets have deliberately not been set. Although all bilateral TEOAE retest failures are obligatory ABR referrals, additional referrals are made directly from parents or paediatricians requesting a measurement of hearing threshold, and it is considered important not to discourage these neonatal referrals. Therefore, although for the 2 y period, a monthly average of 0.9% failed the TEOAE retest bilaterally, a monthly average of 2.5% of those receiving the initial TEOAE screen, received a diagnostic ABR (Figure 4). Only those undertaken because of bilateral TEOAE failure were necessary for the screen aims. The yield with an ABR threshold > 40 dB nHL in the better ear was monitored each month. There were 42 such infants over the 24 months, giving a yield of 4.3=1000 from the total cohort. Only 14 children were con®rmed as having a permanent hearing loss > 40 dB in the better ear. This was a yield of 1.4=1000 of the total cohort. An additional child nursed in the Special Care Baby Unit with hypoxic ischaemic encephalopathy had passed the TEOAE screen, and had not undergone an ABR examination. This single child comprises the Incremental Yield identi®ed to date from this cohort. Outcome monitoring Ultimately the value of early identi®cation must be assessed from improvements in outcome in terms of reduction of disability, but intermediate indicators are used as surrogates of these long-term outcomes. The overall performance of a programme is measured by the distribution of these surrogate outcomes. Cumulative distributions of the ages of identi®cation, con®rmation, referral to the teacher of the deaf, and hearing aid ®tting have been
Figure 4 The TEOAE retest results and the total ABR recipients (as a percentage of number receiving an initial TEOAE test).
Quality of neo-natal hearing screens PM Watkin
recommended. Targets for the detection of congenital deafness have also been set by NDCS Guidelines.20 The nationally set targets are to detect 80% of bilateral congenital hearing impairments within the ®rst year of life, and 40% by six months. The guidelines also recommend that hearing aids should be ®tted within four weeks of con®rmation of hearing loss in appropriate cases. An additional local standard was set after the Whipps Cross 3 y screen evaluation. This revealed a delay between ABR con®rmation of the degree of hearing loss, and the age when both the type and degree of hearing impairment were con®rmed with certainty. This delay, in part, re¯ected inexperience in very early audiological diagnosis of those with a lesser degree of permanent deafness, and thus a standard for achieving audiological certainty by six months was set for those identi®ed by the neonatal screen. The cumulative distributions of the outcomes for the 14 infants identi®ed by the neonatal screen from the 1996, 1997 cohort are detailed in Figure 5. The distributions employ the number identi®ed by the neonatal screen as the 100% level. Although all 14 infants had ABR con®rmation of the degree of hearing loss in Waltham Forest, one had his further audiological diagnosis and hearing aid ®tting undertaken out of district and outcomes were uncertain and thus omitted. A further infant had not been ®tted with hearing aids because of parental non-acceptance of the diagnosis. The target of reaching audiological certainty during the ®rst half of infancy was achieved in 10 of the 13. Similarly of the 12 where the age of hearing aid ®tting was known, exactly half were ®tted with hearing aids within four weeks of the date of audiological certainty. For the remaining half, this NDCS target was not achieved. Had the UNS enabled the achievement of the NDCS target for early identi®cation? Unfortunately this question cannot be answered for several years. Comparison of actual and expected yield suggests that detection over the 2 y audit period has been high. However the incidence of deafness from a limited cohort has wide upper and lower 95% con®dence intervals, and cumulative distributions of outcome can only accurately assess service performance once complete ascertainment has been achieved. For those with a lesser degree of deafness this may not be possible until school entry. This is a critical disadvantage of outcome monitoring.
Discussion The validity and practicability of the universal neonatal TEOAE screen has been widely accepted and the screen is being considered for implementation in many parts of the UK. It offers the advantage of less skilled personnel being employed to undertake the testing. However, in such circumstances routine monitoring is essential. Although outcome monitoring is always necessary to measure the screen worth, it is only possible retrospectively, and this presents real problems for monitoring the performance of a newly implemented hearing screen. Programme success crucially depends upon getting the screen processes right and process monitoring is required to ¯ag up problems at an early stage. The results of the Whipps Cross universal screen have enabled process targets to be set. Clearly, the targets will differ according to the exact screening methodology. However the targets presented should be of use to districts implementing programmes of similar structure. Neonatal screens employing computerised test methods, offer the opportunity of computerised patient data collection. Such databases are now available from the American National Centre for Hearing Assessment and Management (Hi-Screen), and from OZ systems in Dallas (the Screening and Information Management Solution), with the European Concerted Action on OAEs nearing completion (CANS dataset). In the UK neonatal hearing screening data also needs to be entered on increasingly interactive computerised child health surveillance systems. But what is the minimum data set (mds) required? As well as facilitating infant tracking, and reporting programme outcomes, it is essential that the mds enables routine, and preferably automated process monitoring. Conclusions The variations in the incidence of congenital deafness in district cohorts of limited size result in periods when there is no yield from the screen. The implementation of routine quality control reassures that the screen is being correctly implemented during such barren times. Routinised monitoring thus serves as the anxiolytic for the audiologist responsible for the screen.
References
Figure 5 The cumulative distributions of the outcomes for children into a targeted permanent hearing impairment identi®ed from the cohort from January 1996 to January 1998 (n 14).
1 Ewing IR, Ewing AWG. The ascertainment of deafness in infancy and early childhood. J Laryngol Otol 1944; 59: 309 ± 338. 2 Humphries B. The ascertainment and management of defective hearing in the very young. Public Health 1957; 71: 221 ± 228. 3 Howarth IE. Screening tests of hearing in pre-school children with particular reference to selective testing. Med Of®cer 1958; 100: 307 ± 308. 4 Boothman R, Orr N. The value of screening for deafness in the ®rst year of life. Arch Dis Child 1978; 53: 570 ± 573. 5 McCormick B. Hearing screening by health visitors; a critical appraisal of the distraction test. Health Visitor 1983; 56: 449 ± 451. 6 National Deaf Children's Society. Discovering Deafness. NDCS: London, 1983. 7 National Deaf Children's Society. Report on the Initial Process of Diagnosis of Deafness and also follow up Audiology Service. NDCS: London, 1989.
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8 Watkin PM. The age of identi®cation of childhood deafness Ð improvements since the 1970s. Public Health 1991; 105: 303 ± 312. 9 American National Institutes of Health. Early identi®cation of hearing impairment in infants and young children. NIH Consensus Statement 1993 March 1 ± 3; 11: 1 ± 24. 10 Davis AH et al. A critical review of the role of neonatal hearing screening in the detection of congenital hearing impairment. Health Technol Assess 1997; 1(10) full publication. 11 Watkin PM. Neonatal otoacoustic emission screening and the identi®cation of deafness. Arch Dis Child 1996a; 74: F16 ± F25. 12 Watkin PM. Outcomes of neonatal screening for hearing loss by otoacoustic emission. Arch Dis Child 1996b; 75: F158 ± F168. 13 Bennett M, Wade HK. Automated newborn screening using the ARC. In: Disorders of Auditory Function III, Taylor IG, Markides A (eds). Academic Press: London, 1980.
14 Tucker SM, Bhattacharya J. Screening hearing impairment in the newborn using the auditory response cradle. Arch Dis Child 1992; 67: 911 ± 919. 15 Mason J, Herrmann KR. Universal infant hearing screening by automated auditory brainstem response measurement. Paediatrics 1998; 101: 221 ± 228. 16 Kemp DT. Stimulated acoustic emissions from within the human auditory system. J Acoust Soc Am 1978; 64: 1386 ± 1391. 17 Bray P, Kemp DT. An advanced cochlear echo technique suitable for infant screening. Br J Audiol 1987; 21: 191 ± 204. 18 Cochrane AL, Holland WW. Validation of screening procedures. Br Med Bull 1971; 27: 3 ± 8. 19 Haggard M, Hughes E. Screening Children's Hearing. HMSO: London, 1992. 20 National Deaf Children's Society. Quality Standards in Paediatric Audiology. Volume I Ð Guidelines for the Early Identi®cation of Hearing Impairment. NDCS, London: 1994.
Controlling the quality of universal neonatal hearing screens PM Watkin1* 1
Audiology Department, Whipps Cross Hospital, Whipps Cross Road, Leytonstone, London, E11 1NR, UK The Health Technology Assessment Programme has recently reviewed the role of neonatal screening in the detection of congenital hearing impairment. The review recommends that the health visitors distraction screen, currently implemented in the second half of infancy, should be replaced by a national programme based around universal neonatal hearing screening. Such a programme has been implemented as a routine and established service in Whipps Cross Hospital in the East London district of Waltham Forest. This programme has reinforced the need to routinely monitor the screen processes and outcomes. The Whipps Cross audit undertaken over a 2 y period from January 1996 is detailed, as are the targets employed for evaluating the processes. The monitoring ¯agged up implementation problems, and allowed remedial intervention. Monitoring should be built into all the universal neonatal hearing programmes currently being planned in the UK. Keywords: hearing testing; universal neonatal screening; quality monitoring
Introduction For half a century the identi®cation of congenital deafness has been widely accepted as an appropriate aim of public health services in the UK. The 1944 Education Act, and subsequently Section 22 of the 1946 National Health Service Act, provided the impetus for identifying hearing impaired children from birth onwards, but this has remained an elusive goal. By 1952 the distraction test1 was being used by health visitors to screen the hearing of babies during the latter half of infancy.2,3 Widespread implementation followed, but questions about the effectiveness of the Health Visitors Distraction Test (HVDT) were being increasingly voiced.4 ± 7 Even with a sensitive HVDT in place, consistent habilitation for many of those with a congenital hearing impairment has been delayed until school entry and most clinicians and parents consider this to be too late.8 Neonatal hearing screening has therefore reached the agenda. In 1993 the American National Institutes of Health recommended the hearing screening of all neonates, with the aim of introducing habilitation by six months.9 In the UK a recent NHS Health Technology Assessment report entitled `A critical review of the role of neonatal screening in the detection of congenital hearing impairment',10 also recommended universal neonatal hearing screening. This view had been pre-empted by some districts. By 1996, 23 out of 128 districts in England and Wales, were already hoping to implement a universal neonatal screen (UNS). At Whipps Cross Hospital such a screen has been implemented as a routine service since 1992.11,12 In the UK, much has been already been learnt about the trials and tribulations of universal infant hearing screens, and such lessons should not be lost. Importantly, the HVDT screen was not routinely monitored. It therefore took over 25 y of clinical experience, some focused evaluations, and the persistent questioning of the national parents organisation, for its effectiveness to be seriously doubted. However the climate has changed and audit is now routinised into clinical practice. From the outset, on-going monitoring has *Correspondence: Dr PM Watkin, Audiology Department, Whipps Cross Hospital, Whipps Cross Road, Leytonstone, London, E11 1NR, UK. Accepted 28 January 1999
been considered an essential component of the Whipps Cross UNS programme, and the methods employed in this quality control are presented. Universal neonatal hearing screening methods Several testing methods are currently being employed to screen neonatal hearing. The Auditory Response Cradle (ARC) is a microprocessor controlled device which tests the auditory behaviour of neonates.13 It has been used since the early 1980s to screen the neonatal population of a single district in the UK.14 The Auditory Brainstem Response (ABR) has become an established electrophysiological technique for auditory threshold measurement, but it is time consuming, and traditionally this has limited its use to selectively screening a small percentage of the birth cohort at risk of deafness. Automated ABR (AABR) waveform detection has now been developed for screening. Results are more rapidly obtained, facilitating AABR screening of the newborn cohort. This technique is being employed in several American states.15 However it was the description of Otoacoustic emissions at the Institute of Laryngology and Otology, London,16 and the commercial availability of simple recording equipment, that resulted in the resurgence of clinical interest in UNS.17 Otoacoustic emissions are very quiet sounds emitted from the normal cochlea. As long as there is no blockage in the middle or external ear, they can be recorded by a microphone in the ear canal. The simplest way of evoking them is with a transient stimulus such as a click delivered by a miniature speaker sited alongside a recording microphone in an ear canal probe. The recording of transient evoked otoacoustic emissions (TEOAEs) tests the auditory system to the level of the cochlea. However, absence of an emission does not give any information about the degree of impairment and neonates failing a TEOAE screen, require further testing by ABR. The combination of TEOAE testing followed by ABR was recommended by the NIH consensus statement. Although the critical review reported that a combination of TEOAE and ABR is likely to be the optimal method for UNS, recommendation of a speci®c screening system was
172
Quality of neo-natal hearing screens PM Watkin
avoided. In fact the authors considered that given high quality implementation, most combinations of tests could be made effective. In fact there is some commonality in the neonatal screening methods. Importantly, they can all be automated Ð facilitating the undertaking of the screen by less skilled personnel. This is a screening ideal18 which has never been achieved with the HVDT. However when programmes are undertaken by less skilled personnel, issues of routine quality control assume heightened importance. The Whipps Cross screening programme The Whipps Cross programme combines two stage TEOAE testing, followed by threshold ABR measurement for TEOAE failures. It aims at identifying those infants with a bilateral, congenital deafness of moderate degree or worse in the better ear. Although the programme employs only one of several possible test combinations, it mirrors the programme methodology of the HVDT screen, and has proven sustainable and effective for over 5 y. Such a programme has been used in various European centres, and is likely to be further employed in the UK. The constituent processes of the screen are detailed in Figure 1. An initial TEOAE test is undertaken whenever possible before discharge from the Whipps Cross maternity unit. Around 70% of the neonates are discharged within the ®rst 48 h, and unfortunately TEOAE recording at this age may be prevented by the presence of vernix and debris in the ear canal. The optimal test age is after the second day. The programme has therefore built in the further maternity testing of those who failed when initially tested below the optimal test age. These tests (or set of tests for an individual child), are collectively described as the initial TEOAE tests undertaken by the time of maternity discharge. Those missed in maternity and those born out of district or at home are identi®ed at four weeks of age from a register of births recorded on the Regional Interactive Child Health Computerised System (RICHS). They are appointed for their initial TEOAE test in the hospital audiology department, with entry to the screen being offered up to three months of age. All bilateral fails at the initial TEOAE tests are appointed for a TEOAE retest in the audiology department. In line with the aims of the screen, those failing the screen in one ear only are retested on parental request. Bilateral failure at the TEOAE retest prompts an obligatory diagnostic ABR undertaken by a senior audiologist. This test de®nes the degree of hearing impairment. The ABR test is also offered to unilateral failures on parental request, and for other cases of parental anxiety where early diagnosis is required, and also where there is a potential auditory neuropathy. When the ABR threshold is > 40 dB nHL in the better ear, follow up is undertaken within the paediatric audiology department. Here further audiological investigations are undertaken to clarify the type of hearing loss. For those con®rmed with a permanent hearing impairment moderate or worse in degree, the need for habilitation is discussed with the family. The infant is subsequently seen in the combined clinic with the teacher of the deaf, and an intervention programme and home visiting is introduced. Monitoring the screen It has been recommended that outcomes for local cohorts aggregated, for instance, over a 2 y time span, are the most
Figure 1 The Whipps Cross universal neonatal screen programme model.
feasible and accessible measure for monitoring a hearing screening system.19,20 Monitoring the processes involved in the screen has less face validity than measuring outcomes, and may be construed as simple number counting. However if a screening test is of acceptable sensitivity, then the effectiveness of the screen is dependent upon the correct implementation of the processes. Such issues also affect the test failure rate and the screen acceptability. When the condition targeted for detection is of low prevalence a large majority of those failing the screening test will be false positives Ð and these stress the system. A system unacceptably stressed inevitably fails and monitoring correct screen implementation highlights problems before outcomes have been affected over a prolonged period. Such processes need to be measured against standards of acceptable practice. The Whipps Cross programme was evaluated for an initial 3 y cohort of 14 353 infants.11,12 The screen gave a yield of 1.25=1000 with a targeted deafness. The results were used to set standards for subsequent monitoring. The results of the monitoring over a 2 y period for 1996 and 1997 are presented. Throughout the period, the results were fed back to the screeners through regular audit meetings. Monitoring screen processes The processes requiring monitoring, and the performance targets employed in the Whipps Cross audit are detailed in
Quality of neo-natal hearing screens PM Watkin
Table 1 The processes monitored and the targets set Cohort size and coverage (i) All infants eligible for enrolment to be identi®ed and categorised by place of birth and residence (ii) > 95% of each subcohort to receive initial TEOAE test (iii) No bilateral TEOAE fails to be lost to follow up with 100% receiving a further test (iv) > 95% coverage achieved for overall cohort TEOAE testing on maternity (i) > 50% of TEOAE fails on maternity to receive a further test before discharge (ii) > 85% of Whipps Cross births receiving the TEOAE screen to be tested before discharge The results of the TEOAE testing (i) < 10% of initial TEOAE tests to fail bilaterally whether receiving the initial test in maternity or after discharge (ii) < 1% of TEOAE retests to fail bilaterally The ABR tests (i) Diagnostic ABRs to be undertaken on all bilateral TEOAE retest failures, and whenever threshold or neurological testing is requested by parents or other professionals (ii) All those with > 40 dB nHL threshold in the better hearing ear to be referred for further diagnostic assessment within the paediatric audiology department.
Table 1. Achievable targets have been set. Test quality and the accuracy of screener interpretation of pass=fail criteria is checked for a > 10% sample of hardcopied emission recordings on a weekly basis by a senior audiologist. The screen processes are audited for a monthly aggregated cohort of rising six month olds. This time lag allows for completion of the processes for those late screen entrants failing the TEOAE tests and requiring ABR. Monitoring cohort size and coverage Four sub-cohorts are included in the overall screen, and the percentage of infants receiving the initial TEOAE test is audited for each. Coverage is measured as the percentage of all the babies eligible for enrolment who receive the screen to completion. Because of the screen aims, those failing the TEOAE test(s) bilaterally and not attending for the retest in the audiology department, or for the ABR are considered to have reduced the coverage. During the 2 y of 1996 and 1997, the total cohort numbered 9680. The largest of the four sub-cohorts consisted of the 6522 Waltham Forest residents who were born at Whipps Cross. An additional sub-cohort of 1977 Whipps Cross births were not district residents, with 1124 Waltham Forest residents being born either at home or out of district. Fifty-seven babies were neither district residents nor born in Whipps Cross. They were usually staying with relatives, or were resident on the district borders. The percentage of the sub-cohorts receiving the initial TEOAE test is detailed in Figure 2. The small non-district, non-Whipps Cross cohort was not graphically presented, as enumeration implied that the tests had been undertaken. Over the audit period a monthly mean of 97.4% district residents and 96.6% non-district residents born at Whipps Cross received the initial TEOAE test. The > 95% target was always achieved for the former subcohort and achieved two thirds of the time for the latter. However, despite increased publicity and professional awareness training, the target was never achieved for Waltham Forest residents who were not born at Whipps Cross. Up to March 1997, a monthly average of 71% of this sub-cohort had received the test. After this the universal HVDT was dropped in the district, and for the remaining nine months of the audit period, an average of 83% received the initial test with the target still not being achieved in any month. The reasons were investigated and attributed to two factors. A minority of parents were
Figure 2 The percentage of the cohorts receiving the initial TEOAE test and the overall coverage.
reluctant to attend Whipps Cross, when they had elected to have their babies born elsewhere. There was also incomplete referral of babies moving into the district up to three months of age. The inadequate enrolment of this sub-cohort reduced the overall coverage. The bilateral TEOAE test failures not completing the programme also reduced the coverage, but in fact this number was small (mean of four per month), with a monthly average of 91.8% of those failing a TEOAE test bilaterally, receiving a further test. Inadequate enrolment, rather than large losses to follow up, was the main factor resulting in a disappointing, monthly average coverage of 93.7%. Only 3 of the 24 monthly cohorts achieved the coverage standard of > 95%. Further measures to improve enrolment of district residents not born in Whipps Cross, are necessary for this standard to be consistently achieved. Such strategies are being planned. Monitoring TEOAE testing on maternity Auditing the percentage of Whipps Cross births who receive their initial TEOAE test before discharge, ensures adequacy of screener input to maternity. A target of > 85%
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was set from the 3 y evaluation. This was achieved for one third of the months audited in 1996 and 1997. A monthly average of 83.3% of the babies born at Whipps Cross were tested before discharge. An enthusiastic high of 90.7% was achieved early in 1996, with a low of 70.9% recorded for the holiday month of August 1966. Action was taken to support maternity testing over the holiday period the following year. There were also ¯uctuations in the further maternity testing of those failing the TEOAE test when initially tested at a sub-optimal age. The target set from the 3 y evaluation was that 50% of such initial test failures should receive a further TEOAE test by the time of maternity discharge. This target was only achieved for one third of the months audited. Monitoring the crude failure rates of the TEOAE tests The failure rates of the initial TEOAE tests undertaken in maternity by the time of discharge, and in the audiology department, are monitored. The results of the initial TEOAE tests undertaken by the time of maternity discharge, combined with the results of the initial TEOAE tests undertaken after discharge, are detailed in Figure 3. A target of < 10% for bilateral failure at the initial TEOAE test was set from the 3 y evaluation. In line with the aims of the screen a target for unilateral TEOAE failure was not set, although it is still monitored. The average monthly bilateral failure rate was 10.5% with the target of < 10% being achieved for half of the audit months. In addition to those failing bilaterally, a monthly average of 13.9% failed the initial TEOAE test unilaterally. The crude failure rate of the initial tests undertaken in maternity and after discharge, were separately monitored. As expected, the failure rate for the initial TEOAE tests after discharge was relatively low, and in all but one month the target was achieved for both unilateral and bilateral failure. Higher failure rates were experienced when the initial TEOAE tests were undertaken in maternity. From March 1996 for the rest of that year, there was an average monthly maternity bilateral failure rate of 15.7%. Staf®ng changes early in 1997 reduced this and thereafter the bilateral rate once again achieved the target.
Figure 3 The crude failure ratio of the initial TEOAE tests.
The results of the TEOAE re-tests are detailed in Figure 4. The average monthly bilateral TEOAE retest failure rate was 0.9%, with an additional 1.5% failing unilaterally. The target of < 1% failing the retest bilaterally was achieved in exactly half of the months. ABR Tests These tests were monitored each month. However targets have deliberately not been set. Although all bilateral TEOAE retest failures are obligatory ABR referrals, additional referrals are made directly from parents or paediatricians requesting a measurement of hearing threshold, and it is considered important not to discourage these neonatal referrals. Therefore, although for the 2 y period, a monthly average of 0.9% failed the TEOAE retest bilaterally, a monthly average of 2.5% of those receiving the initial TEOAE screen, received a diagnostic ABR (Figure 4). Only those undertaken because of bilateral TEOAE failure were necessary for the screen aims. The yield with an ABR threshold > 40 dB nHL in the better ear was monitored each month. There were 42 such infants over the 24 months, giving a yield of 4.3=1000 from the total cohort. Only 14 children were con®rmed as having a permanent hearing loss > 40 dB in the better ear. This was a yield of 1.4=1000 of the total cohort. An additional child nursed in the Special Care Baby Unit with hypoxic ischaemic encephalopathy had passed the TEOAE screen, and had not undergone an ABR examination. This single child comprises the Incremental Yield identi®ed to date from this cohort. Outcome monitoring Ultimately the value of early identi®cation must be assessed from improvements in outcome in terms of reduction of disability, but intermediate indicators are used as surrogates of these long-term outcomes. The overall performance of a programme is measured by the distribution of these surrogate outcomes. Cumulative distributions of the ages of identi®cation, con®rmation, referral to the teacher of the deaf, and hearing aid ®tting have been
Figure 4 The TEOAE retest results and the total ABR recipients (as a percentage of number receiving an initial TEOAE test).
Quality of neo-natal hearing screens PM Watkin
recommended. Targets for the detection of congenital deafness have also been set by NDCS Guidelines.20 The nationally set targets are to detect 80% of bilateral congenital hearing impairments within the ®rst year of life, and 40% by six months. The guidelines also recommend that hearing aids should be ®tted within four weeks of con®rmation of hearing loss in appropriate cases. An additional local standard was set after the Whipps Cross 3 y screen evaluation. This revealed a delay between ABR con®rmation of the degree of hearing loss, and the age when both the type and degree of hearing impairment were con®rmed with certainty. This delay, in part, re¯ected inexperience in very early audiological diagnosis of those with a lesser degree of permanent deafness, and thus a standard for achieving audiological certainty by six months was set for those identi®ed by the neonatal screen. The cumulative distributions of the outcomes for the 14 infants identi®ed by the neonatal screen from the 1996, 1997 cohort are detailed in Figure 5. The distributions employ the number identi®ed by the neonatal screen as the 100% level. Although all 14 infants had ABR con®rmation of the degree of hearing loss in Waltham Forest, one had his further audiological diagnosis and hearing aid ®tting undertaken out of district and outcomes were uncertain and thus omitted. A further infant had not been ®tted with hearing aids because of parental non-acceptance of the diagnosis. The target of reaching audiological certainty during the ®rst half of infancy was achieved in 10 of the 13. Similarly of the 12 where the age of hearing aid ®tting was known, exactly half were ®tted with hearing aids within four weeks of the date of audiological certainty. For the remaining half, this NDCS target was not achieved. Had the UNS enabled the achievement of the NDCS target for early identi®cation? Unfortunately this question cannot be answered for several years. Comparison of actual and expected yield suggests that detection over the 2 y audit period has been high. However the incidence of deafness from a limited cohort has wide upper and lower 95% con®dence intervals, and cumulative distributions of outcome can only accurately assess service performance once complete ascertainment has been achieved. For those with a lesser degree of deafness this may not be possible until school entry. This is a critical disadvantage of outcome monitoring.
Discussion The validity and practicability of the universal neonatal TEOAE screen has been widely accepted and the screen is being considered for implementation in many parts of the UK. It offers the advantage of less skilled personnel being employed to undertake the testing. However, in such circumstances routine monitoring is essential. Although outcome monitoring is always necessary to measure the screen worth, it is only possible retrospectively, and this presents real problems for monitoring the performance of a newly implemented hearing screen. Programme success crucially depends upon getting the screen processes right and process monitoring is required to ¯ag up problems at an early stage. The results of the Whipps Cross universal screen have enabled process targets to be set. Clearly, the targets will differ according to the exact screening methodology. However the targets presented should be of use to districts implementing programmes of similar structure. Neonatal screens employing computerised test methods, offer the opportunity of computerised patient data collection. Such databases are now available from the American National Centre for Hearing Assessment and Management (Hi-Screen), and from OZ systems in Dallas (the Screening and Information Management Solution), with the European Concerted Action on OAEs nearing completion (CANS dataset). In the UK neonatal hearing screening data also needs to be entered on increasingly interactive computerised child health surveillance systems. But what is the minimum data set (mds) required? As well as facilitating infant tracking, and reporting programme outcomes, it is essential that the mds enables routine, and preferably automated process monitoring. Conclusions The variations in the incidence of congenital deafness in district cohorts of limited size result in periods when there is no yield from the screen. The implementation of routine quality control reassures that the screen is being correctly implemented during such barren times. Routinised monitoring thus serves as the anxiolytic for the audiologist responsible for the screen.
References
Figure 5 The cumulative distributions of the outcomes for children into a targeted permanent hearing impairment identi®ed from the cohort from January 1996 to January 1998 (n 14).
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