Currently, the main hearing screening instruments used in China are otoa-coustic emissions (OAE) and automated auditory brainstem response (AABR). The results of the screenings are indicated as "pass" or "fail". In general, the sensitivity and specificity of OAE and AABR can reach more than 95%, while OAE is slightly lower than AABR.
1. Otoacoustic emission: Otoacoustic emission is the reverse of the usual process by which sound waves are transmitted to the inner ear, whereby acoustic energy generated in the cochlea passes through the middle ear structures and then through the tympanic membrane, entering the outer hair cells of the cochlea, where the energy is reflected back out of the cells and is recorded in the external auditory canal. Otoacoustic emissions are categorized into spontaneous otoacoustic emissions (SOAE) and evoked otoacoustic emissions (EOAE) according to the presence or absence of external acoustic stimuli, and the latter are categorized into transient evoked otoacoustic emissions (TEOAE), distortion-product otoacoustic emissions (DPOAE) and frequency-stimulated otoacoustic emissions (SFOAE) according to the type of stimuli. Otoacoustic emissions are closely related to inner ear function, and any factor that impairs the function of the outer hair cells of the cochlea that results in hearing impairment above 40 dBHL can lead to a significant reduction or loss of otoacoustic emissions. Furthermore, otoacoustic emission is a non-invasive technique that is easy to perform and takes only 10 minutes to test both ears. Since TEOAE and DPOAE can be elicited in almost all normal ears, SOAE is only recorded in 50-60% of normal ears. Therefore, TEOAE and DPOAE are commonly used in newborn hearing screening.
2. Automated Auditory Brainstem Evoked Potentials (AABR): A rapid, noninvasive ABR test using a specialized test probe. The AABR technique was developed and used in conjunction with the OAE technique to screen the cochlea, the auditory nerve conduction pathway, and the brainstem. Newborns with risk factors for hearing loss are more likely to have postcochlear lesions. If OAE is used alone, cochlear lesions may be missed. Therefore, newborns with risk factors for hearing loss should be screened with a combination of OAE and/or AABR to avoid miss-screening for this disease.