Autism may or may not be a medical condition

Gus the Fuss has posted a snippet of a quote from Simon Baron-Cohen (who seems to have turned into some kind of bogeyman for the JABS crowd recently) which includes the line:

Because autism is a medical diagnosis, it shouldn't be given out lightly

Gus has picked up on this line, but I have no idea what he's arguing when he says this:

If autism is a medical diagnosis why is there no protocol of medical testing in place---blood/urine/stool/hair?

He appears to be saying autism isn't a medical condition - which, coming from the father of an autistic son is rather odd. He also appears to be saying that every condition should be testable by looking at something physical. So is he denying the existance of (for example) Alzheimer's? Clinical depression? I really haven't the foggiest idea what point he thinks he's making.

(I suppose it's possible he just can't stand Professor Baron-Cohen, and so feels he has to disagree with every statement he makes…)