I'm not exactly sure which tests you've gotten. It may be the case that the audiologist will only test a few frequencies for someone who is likely to have good hearing. But if you are fitted for hearing aids they will test a range of frequencies from 100 Hz to 8000 Hz.
Almost all cases of hearing loss have hearing loss at high frequencies, so they may be able to screen you by just checking at higher frequencies. As far as I know, losing bass frequencies first only comes from specific conditions like Meniere's disease.
8K seems too low. Sure at 20K you wouldn't hear anything, but there's still a lot of potential to hear a low level hum at let's say 13K which drives you mad.
Almost all cases of hearing loss have hearing loss at high frequencies, so they may be able to screen you by just checking at higher frequencies. As far as I know, losing bass frequencies first only comes from specific conditions like Meniere's disease.