This happened to a bloke at work after he was 'too honest' on the medical questionnaire. He had the blood test and assumed that would be the end of it, turned out his liver tests showed areas of concern and CASA decided he was a full blown alcoholic despite several specialists giving him letters to say he had a genetic liver issue which results in elevated liver results. Basically he was off work for 9 months as despite the specialist evidence CASA were not happy bunnies and stated it was up to him to 'prove he wasn't an alcoholic'.
End of the day the lesson is, be very very very careful how you answer those questions.