thanks for query
its very early to say thats ur son has CF only from above 2 findings
dont be worried
look for the following things
the taste of the sweat of ur son
is he suffering from frequent chest infections??
is there any frothy diarrhoea?
polyp can be explained by other diseases also
consult with the other doctors
do the following test
sweat chloride test
x-ray of para-nasal sinuses
thorax if chest x-ray is suggestive or inconclusive