Neonatal hearing screening in an at-risk population using a highly automated ABR test is a viable and effective tool for identification of hearing impairment. Although the field sensitivity of the test is high, it is unable to identify all babies with a criterion level of hearing loss. There are a number of possible explanations as to the origin of false negative results: configuration of the pure-tone audiogram, a progressive hearing loss, acquired sensorineural or conductive loss, retrocochlear deafness, or an incorrect interpretation of the screening test. Passing a neonatal screening test, therefore, does not exclude the possibility of subsequent hearing impairment and highlights the need for further surveillance.
The desirability of finding children with hearing impairment after bacterial meningitis as soon as possible prompted us to examine the feasibility of using evoked otoacoustic emissions (EOAE) as an in-patient check of hearing status in children recovering from bacterial meningitis. Sixty-six episodes of bacterial meningitis were studied. Traces could be recorded for only 54.7% of ears. All children subsequently found to have sensorineural hearing impairment who were tested with EOAE, failed the screening test. The low coverage of the screening test and the predicted low specificity due to the high incidence of conductive hearing impairments, lead us to conclude that, with the technology currently available, the measurement of EOAE after bacterial meningitis is not a practical method for a pre-discharge check of hearing. Every effort must still be made to ensure all children are referred for an appropriate auditory assessment.
Transiently evoked otoacoustic emissions (TEOAE) and auditory brainstem response (ABR) tests were used in parallel to screen 862 neonates with risk factors for hearing loss. Seven neonates (0.81%) passed on TEOAE screen yet failed on ABR in one ear (six neonates) or both ears (one neonate). This combination of results has been termed 'anomalous'. Examination of audiometric results obtained on follow-up shows that in one ear of one neonate the result was consistent with the later confirmed audiogram shape. The explanation for the anomalous results in the remaining ears is unclear although neural maturation and the effects of hyperbilirubinaemia are possibilities. There were no instances of progressive or retrocochlear hearing loss identified. None of the seven neonates had better ear hearing loss of > or = 40 dB on long term follow-up.
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