Hey guys
The above is correct. However, if you use a medikit by accident or pick one up by accident, you don't have to do a full runthrough again. I did Act 1, stage 1 and 2 and the whole of Act 2 and 3 without using a kit. However, I thought I had to do another runthrough again. I finished Act 1 and the cheevo popped. You only have to redo the Act you used a kit on.
Should save you all some time when you think of doing another run.