Autism itself does not affect the quality or safety of your blood. 

Two issues that might pop up: -

- Any medication you are taking (they do ask about medications).

- If you have any difficulty verbally expressing consent.  In addition to written consent (when I last donated blood) verbal confirmation was required.   Even then I am sure there would be work-arounds available via taking a support person with you.

On that last point I obviously don't know how autism personally affects you and I'm not assuming anything. I'm just aware from people I do know that it has a broad spectrum of effects.

All the best and good on you for donating.