Depending on the school it might not count as college credits. I took my CNA course through continuing education and I received 80 contact hours, but no credits.
The only thing required for my course was the mantoux (TB) test. Which you can get from your doctor or the college's student health center. As far as classes nothing is required. CNA courses are pretty straight forward and rather simple. It's a lot of common sense mixed up with a few facts and a few skills.