Right now if you are going strictly by the DSM or ICD there is no such diagnosis as HFA or LFA. Just autism, Asperger, childhood disintegrative disorder, PDD-NOS, and Rett's.
But some doctors will write high or low functioning or mild or severe. But technically the diagnosis is just autism.
Soon the DSM will have all of those things called just autism, and Rett's will be removed. Autism will be rated from mild to severe though, on the basis of a few traits that are not even really central to autism. (But not on the basis of IQ or academic ability either.)
I just have a diagnosis of autism. No high functioning attached. Occasionally people have attached low functioning or severe, but only in side comments, not in the diagnosis itself usually. I don't believe in functioning levels, and I don't think we know enough about what autism is to tell the difference between mild and severe. So I just go by autistic. I think I have a particular non-majority subtype but there is no name for it officially.
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"In my world it's a place of patterns and feel. In my world it's a haven for what is real. It's my world, nobody can steal it, but people like me, we live in the shadows." -Donna Williams