Registration of otoacoustic emissions (OAE) and auditory brainstem evoked potentials (ABR) have become a standard in neonatal hearing screening and are used worldwide. These methods are recommended as the tools in neonatal hearing screening programms (3, 4).

For over 10 years, ABR has been a „golden standard” in neonatal hearing screening. The sensitivity and specificity of this test are close to 100%. In neonatal hearing screening, 2 modes are applied: conventional ABR using intensity sequences, and automated ABR. In the conventional method, the threshold of wave V is investigated. In full-term newborns the threshold is 30 dB nHL. The test outcome is assessed subjectively by the tester. In the automated mode, both the registration process and evaluation of the result are performed automatically. In the automated mode, the presence of wave V is usually assessed for only one intensity level (most commonly 35 dB nHL). The advantages of ABR as a screening test are its high sensitivity and specificity, and the possibility of assessing both the sensory part and a substantial portion of the neural part of the auditory pathway. The disadvantages of ABR are the relatively long duration of the test, and subjective assessment of the result when using the conventional mode. ABR is also a basic method in establishing a diagnosis of hearing loss in a child.

The second most popular hearing screening tool in newborns and infants is otoacoustic emission. In hearing screening programmes, two kinds of emissions are used. They are transiently evoked otoacoustic emissions (TEOAE) and distortion product otoacoustic emissions (DPOAE). Most screening programmes use TEOAE, but recently DPOAE has become more and more popular. The advantages of the OAE test are its high sensitivity and simplicity. The disadvantage is the high susceptibility of the test result to environmental noises or internal noise produced by the child. OAE is not correct for identifying retrocochlear lesions. However, pure retrocochlear hearing loss is relatively infrequent in the newborn population (according to White, no more than 1% of all hearing impaired children, or 3 cases in 100000 persons in the whole population) (7).

The aim of this study is to discuss the applicability of OAE and ABR techniques in newborn and infant screening for hearing loss, based on the experience of the Department of Audiology of the Institute of Physiology and Pathology of Hearing in Warsaw.

In the period from September 1997 till February 1999, in the screening section of the Department of Audiology of the Institute of Physiology and Pathology of Hearing, 540 newborns and infants aged 0-7 months have been tested. All have been referred for a screening test after discharge from the neonatal ward due to the presence of risk factors for hearing loss found either in the neonatal period or in the subsequent months of life. The presence of risk factors was assessed using a questionnaire developed at the Institute of Physiology and Pathology of Hearing, based on the recommendations of the Joint Committee on Infant Hearing (3). Before the screening test was performed, the medical history of the child was taken, with special attention to risk factors for hearing loss. The information on the child´s auditory reactions was also obtained. The children were tested using either OAE or conventional ABR. OAE tests were performed using the Quickscreen option in the ILO 88 device. ABR tests were performed using a Polish KUBA device. Additionally, behavioural tests were carried out on in children using a BabyMeter device or musical instruments of known frequency. When interpreting TEOAE tests, the Rhode Island Hearing Screening Project criteria are used (5). The result of the test was considered as normal when the correlation factor for 1.6 kHz was at least 50% and for 2.4, 3.2 and 4kHz was at least 70%. If the value of the correlation factor was lower than the target values for at least one frequency, the child was referred to diagnostic ABR. The result of the ABR test was considered normal if wave V was present for intensity level 30dB nHL. If the threshold of wave V was higher than 30 dB nHL, the child was referred to diagnostic ABR as well. Diagnostic ABR was performed using an Eptest device.

491 newborns and infants were screened using TEOAE. 116 of them (24%) failed the screening test. Diagnostic ABR was performed on all of them. Based on the result of diagnostic ABR, 27 children were identified as having hearing loss, which constitutes 23% of children who failed the TEOAE screening test and 5% of children screened initially with TEOAE.

49 children were screened using ABR. 11 of them (22%) failed the screening test. Based the diagnostic ABR, hearing loss was identified in 6 children which constitutes 54% of children who failed the screening test and 12% of children screened initially with ABR.

Referral rates for TEOAE and ABR tests were similar (24% and 22% respectively). These values seem to be higher than those cited in the literature (6). However, in some centres, even higher referral rates of 40% and more have been obtained (1, 2). The data described in the literature were obtained mostly from neonates in the first 72 hours of life, while in our centre we have mostly tested infants older than 1 month. Our experience shows that performing a screening test in an infant is more difficult due to the higher activity of the child which may interfere with the screening test or even unable the test performance.

The number of children identified with hearing loss was relatively high. In the group tested with TEOAE, hearing loss was found in 1 of 4 children referred to diagnostic evaluation. In the group tested with ABR this ratio was even higher and was 1 case of hearing loss in 2 children referred to diagnostic evaluation. Generally, in the whole group tested with TEOAE, hearing loss was found in 5% of children. This number is in accordance with the data cited in the literature concerning the prevalence of hearing loss among children at risk (4). In the group tested with ABR hearing loss has been identified in 12% of children. This relatively high number may result from the fact, that children were referred to ABR screening test when the risk for hearing loss seemed to be relatively high i.e. multiple risk factors or neurological disorders were present. Therefore the group tested with ABR were children a with higher risk of hearing loss than in the other children at risk.

OAE and ABR tests are currently widely used in the hearing screening of newborns and infants. Both tests show high sensitivity and specificity. Referral rates both in OAE and ABR tests seem to be higher in infants than in newborns, due to the activity of the child. However, both tests are applicable and efficient in screening infants for hearing loss.