LEED NC or HC?

6,000 sf existing LEED NC V2.2 certified. 3,000 sf (Max) addition The entire existing building and proposed addition is a outpatient healthcare operation. I don’t know if it is licensed or not. We want the addition to be LEED certified as well. At this point we the best approach to this is to only certify the addition and leave the existing alone. We should be able to do this since the mechanical systems are separate from the existing, etc. Do I use LEED NC or LEED HC or do I have a choice (we are past the Jan 1 2012 date)? Thank you very much, Lee