A hearing loss above 8,000 Hz. It can only be detected using a special audiometer calibrated to test hearing in the frequencies between 8,000 and 20,000 Hz. Conventional hearing testing only tests those frequencies between 125 and 8,000 Hz. Many ototoxic drugs cause sub-clinical hearing loss, at least in the beginning. That is why sub-clinical testing is so important, yet it is seldom done.
Sub-clinical Hearing Loss