In my opinion if he has a Dx of ADHD he already has a Dx of ASD as in all but current official classifications and narrow minded professional mindsets, ADHD is an autistic condition. Most of these sub-classifications will be fall out of use, DSM has dropped Aspergers, more will follow.
I also believe that most if not all Dx of “bipolar” will change again, also fall into the ASD umbrella when a more specific and truly diagnostic test is available – as one day it surely will be.
Not wishing to upset anyone or indeed start some form of tribal or elitist war but one has to remember that Asperger himself was characterising a subset of individuals described as “Autistischen“, he himself describing a less serious form. So I think in this case DSM V is kind of clarifying matters (not to say I completely agree with it!).
However, I am vehemently against all the labels across the entire Autistic Spectrum, society and the medical and allied fraternities can have some pugnacious attitudes to the word autism. I wish the whole use of all the words would just go away in a diagnostic sense and come up with something completely different maybe simply PDD?