False Negatives with Screening OAE

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Answer

An answer this question requires a study that is likely never to be conducted. False negatives, false positives, true negatives and true positives can be accurately determined only if EVERY subject first received a complete diagnostic evaluation, generally a very long evaluation at birth under sedation with the final diagnosis determined by an audiologist and based on an integration of all of the audiologic test results. For neonates, 1000 would have to be tested to find 3 to 6 with an actual hearing impairment so it would not be justifiable to put so many normal hearing babies through such an ordeal. However, this is the only way to determine which baby is truly hearing impaired and which is truly normal hearing. After all of these diagnostic tests were performed, then the screening test could be performed on all to find out if any of the hearing¬impaired babies received a "Pass" on the OAE screening test.

Another consideration is the fact that a baby's hearing status is not necessarily static. Many babies are born with normal hearing and then acquire a hearing loss after birth because of genetic factors (progressive hearing loss, e.g.) or a large number of external factors such as infections, ototoxic drugs, etc. Even a baby who passed the OAE screen at birth and was then found to be deaf at age 3 months cannot be legitimately identified as a false negative because the baby may have had normal hearing at birth and become deaf due to a progressive hearing loss. One very rare exception to this may be a situation where the deafness diagnosed after the OAE screening test was definitively linked to a condition that unquestionably existed before the OAE test such as a gross cochlear deformity. I am not aware of any such cases reported so far.

The hearing impaired auditory system does not produce the characteristic signals that the normal auditory system produces, an otoacoustic emission or a characteristic waveform from scalp electrodes. In the case of OAE screening, it is almost impossible for a device to determine that the signal coming from the hearing impaired ear contains characteristic emissions that in fact are not there. Even so, as a precaution, I always have with me a test cavity (one supplied by the manufacturer or even the cap of a ball point pen). I then often perform the screening test on this "deaf" cavity to reduce the possibility of the device giving it a "Pass" and therefore a false negative.

Dr. Gerald R. Popelka has conducted auditory research at Washington University and Central Institute for the Deaf for 24 years. He recently joined the faculty at Stanford University and is now investigating the relation between hyperbilirubinemia and auditory system development in neonates.