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The true answer is "You just don't know" - until they share something that they will be very coy about ... which is the percentage rate of "false positives".
Say they eventually admit that this is about 2% of people scanned (not a bad rate actually).
This then means that (if you get a positive result) your actual chance of having the illness is ... about 33%. Not the 99% that they waved at you in the first place.
[ explanation :
scan 1,000,000 people
10,000 will have the illness and 9,900 will be given a (true) positive diagnosis
990,000 will not have the illness - 19,800 will be given a (false) positive diagnosis
you have an 1 in 3 chance of being in the 'true' group ]