Universal newborn hearing screening (UNHS) is now performed worldwide because of the significant harm of unidentified permanent congenital hearing loss. These hearing screening programs have shown benefits for newborns and the Joint Committee on Infant Hearing (JCIH) has renewed up-to-date guidelines for hearing screening using automated auditory brainstem response (AABR) and/or evoked otoacoustic emission (EOAE) (1, 2). These protocols, performed according to the JCIH guidelines, have yielded successful results (3-7).

Among the drawbacks of UNHS is the excessive number of false positives (i.e., normal ears falsely found to have hearing loss) detected using these protocols. About 60-80% of infants referred for further testing were found to be false positives, increasing the rates of medical interventions (3-6). Thus, it is important to reduce the referral rate itself as much as possible. Because UNHS protocols using AABR generally have lower referral rates and better positive predictive values than protocols using EOAE, many institutions utilize AABR protocols (5-7).

Another concern of these screening protocols is the possibility of a change in hearing status after screening protocol. Infants with late onset hearing loss would not be detected by UNHS, suggesting that infants with risk indicators proposed by the JCIH should be rescreened (1). Furthermore, although few follow-up audiology studies after confirmation of congenital hearing loss have been performed, some studies reported children with congenital permanent sensorineural hearing loss undetected with newborn hearing screening (8, 9). Conversely, infants with confirmed hearing loss showing later improvements in hearing were reported (10).

How to confirm congenital hearing loss after newborn screening is another issue. Conventional click air conduction auditory brainstem response (ABR) has been used as a diagnostic method in many previous studies (3-6). Since conventional click ABR may give limited information in differentiation between permanent and temporary, or sensorineural and conductive hearing loss, use of bone conduction ABR in evaluation of failed newborn hearing screening has been reported (8, 11, 12). We have operated a newborn hearing screening program using staged AABR since 2004 with conventional click ABR testing, which is considered to be examined in terms of feasibility with extended follow-up.

We therefore investigated the validity of newborn hearing screening method using AABR, click ABR testing and tympanometry protocol and we also evaluated changes in hearing status of infants with confirmed congenital hearing loss.

We screened 90% of healthy newborns for UNHS over a period of about 6 years, with nearly 80% of referred neonates followed up for confirmation. Although our protocol did not reach a capture rate of 95% or a follow-up rate of 90%, the quality indicators of the JCIH in 2007, we consider our rates remarkable for Korea, a country where newborn hearing screening is not fully supported by the national health insurance service (1). The referral rate was 1.36%, with 45 true positives and 72 false positives identified through the screening protocol. Thus, of over 10,000 infants screened, 0.41% was true positives of screening results, and the positive predictive value of our protocol was 38.46%, both of which are acceptable and comparable with other studies (3-7, 10). Thirteen infants (0.12%) had greater than moderate hearing loss bilaterally, requiring hearing rehabilitation; this incidence of congenital hearing loss was similar to those shown previously (3-7, 10).

Follow-up ABR was performed to assess the initial diagnostic ABR result and the accuracy of the first diagnosis. Of 34 infants followed up serially, about one-third had normal hearing status during follow-up ABR, indicating that the cases, initially regarded as having hearing loss judged by diagnostic ABR, were actually normal in hearing. Moreover, of the subjects with hearing loss on diagnostic ABR, some infants showed changes in severity of hearing loss on follow-up ABR. Such normalization of hearing or changes in severity of hearing loss was noticeable in subjects with mild or moderate hearing loss. Of the 6 subjects with mild hearing loss on diagnostic ABR, none had hearing loss on follow-up and only 4 of 9 subjects with moderate hearing loss on diagnostic ABR were found to have hearing loss finally. In contrast, subjects with severe or profound hearing loss on diagnostic ABR showed relatively robust results on follow-up.

One of the possible causes of the change of hearing level may be related to the middle ear inflammation. Considering the incidence of middle ear effusions in infancy is estimated to be as high 61%, subjects with middle ear effusion can be involved in our study population (13). Actually, middle ear opacity on high resolution computed tomography (HRCT) has been reported in about 40% of infants with bilateral hearing loss of more than 50 dB identified by newborn hearing screening (10). Another possible explanation of hearing improvement can be delayed auditory pathway maturation. Talero-Gutierrez et al. (14) reported spontaneous recovery of hearing threshold in children around 1 year of age.

The key point of distinguishing temporary hearing loss due to middle ear effusion from permanent congenital hearing loss is complete evaluation for middle ear pathology. For this purpose, we used otoscopic examination and 226 Hz tympanometry which have substantial limitation for clear conclusion. Physical examination of the tympanic membrane in infants may be inaccurate due to technical difficulties, such as narrow ear canals, the presence of cerumen, and the lack of cooperation, and may also contribute to a misdiagnosis of middle ear effusion (15, 16). Furthermore, a study of infants less than 7 months old demonstrated that the result of tympanometry is often normal in the presence of middle ear effusion (17). In addition, standard 226 Hz tympanometry may not be appropriate for hearing screening in infants less than 6 months of age because of its incorrect and unreliable results and the JCIH has recommended that these infants be screened by 1,000 Hz tympanometry (1, 18, 19). If temporary middle ear effusion resolved during follow-up, follow-up ABR would show normal results. Because we performed only air conduction click ABR testing and 226 Hz tympanometry throughout follow-up, it might not be able to detect middle ear effusion in considerable number of subjects. Thus, undetected middle ear effusion at the time of diagnostic ABR may explain our temporary hearing loss findings.

In addition, we identified 9 ears that passed initial AABR screening and proved as having hearing loss on diagnostic ABR. Since none of these infants was suspected of having middle ear effusion at the time of diagnostic ABR, they could be regarded as having undetected congenital hearing loss which could threaten the feasibility of newborn hearing screening protocols. However, because all the patients except one showed normal hearing during follow-up and one of these patients was follow-up loss, there was no false negative case found in our series.

Change of hearing thresholds on follow-up ABR testing draws attention to the need of clear discrimination of type of hearing loss at the time of diagnostic testing. Many previous studies have concentrated on methods and results of the screening procedure and provided less information about the confirmation method and how to they clearly exclude the temporary conductive hearing loss (3-6). As seen in this study, however, conventional click ABR and 226 Hz tympanometry are not enough to evaluate all possible hearing conditions. Some recent studies implemented bone conduction click or tone burst ABR with/without 1,000 Hz tympanometry in evaluation of failed newborn hearing screening and it can bring proper early diagnosis by distinguishing amongst permanent sensorineural hearing loss, permanent conductive hearing loss, and temporary conductive hearing loss (8, 11, 12).

JCIH guidelines have emphasized that hearing interventions be performed before 6 months of age, and there is increasing interest in the benefits of auditory rehabilitation for unilateral or mild bilateral hearing loss (1, 20, 21). Excessive false positive cases due to middle ear effusions can result in additional unnecessary medical interventions, put an emotional burden of parents and lower the specificity and positive predictive value of the screening method. Our results indicate that hearing status at the time of diagnostic testing is uncertain with conventional click ABR and 226 Hz tympanometry, especially in cases of mild to moderate hearing loss and raise the need for implementation of more tools for bone conduction and middle ear evaluation to clarify whether temporary hearing loss of our study is temporary conductive or sensorineural hearing loss.

Taken together, the referral rate and the positive predictive value of our protocol were acceptable. We have also found here that substantial temporary hearing loss can be included in the first confirmative diagnosis. Temporary hearing loss of our study on follow-up give emphasis to need of further differentiation using the testing for bone conduction and middle ear status. Complete evaluation of type and severity of hearing loss is important to avoid excessive burden from follow-up and to provide proper early intervention for permanent hearing loss.