You can be severely autistic and that can be HFA
But you can't have HFA and severe autism: it's one of the other
DS1 has severe Aspergers: tests are so basic in their definitions that they don't measure severity, only presentation.
As an example (simplified but ykwim):
Autism is triad of impairments plus language delays and IQ showing learning difficulties
HFA is language delays and triad but average to high IQ
AS is no language delays or IQ under 60 but triad
Now, is a child is very severely sensory affected, or aggressive, or even has an IQ of 62 theya re still severer but don't meet qualifying criteria for diffeent areas
Do you see?
DS1 as a child of ten needing 24/7 supervision even via a TA at breaktimes is in relaity a child severely affected by his ASD; most kids his age are able to walk home, grrab lunch and alk back and they all will do so in a year at comp....... nto ds1 though, not a chance.
Does that make sense?
Apart from straightforward 'classic' autism which requires severe LD, the dx's make no assumptions as to severity of affectation and are simply a label of description.