As far as I can tell any abnormality whatsoever has to be reviewed by a specialist. I THINK most of the time these are dismissed, sometimes you get asked back for a sleep deprived test. The technician told me not to worry too much as loads of people get referred to a specialist but they only fail between 6 or 8 people a year on the EEG out of about 1200.
I say THINK as I'm still waiting on a specialist to review mine!