The use of the word "savant" and "disabilities" and the suggestion of testing at such a young age makes me think that your pediatrician wants your son tested for autism, rather than for giftedness. Here's hoping that the result is "it's OK, he's not autistic, just gifted" but you certainly can't expect to get good information about how gifted at this age. If I were you, I would present the testing to other people (if you need to mention it at all) as being to rule out autism, anyway; that's much easier for people to accept, I think.
Do you have any concerns in that direction yourself? If you feel absolutely confident that there's nothing going on except giftedness, you might want to turn down the testing.
