Just a heads up that this may not be the case for everyone. I have an ACA plan and while the PCP visit was free, the blood test he ordered was not. There's still some confusion about exactly what's covered and what's not, and it sounds like it could change over time.
Sorry, to be clear -- an annual PCP visit may result in the doctor ordering a blood test that you have to partially pay for, depending on what the doctor thinks needs to be done following his/her examination of you.
Basic blood work of a preventative-care nature, such as HDL/LDL ratio, triglycerides, etc, is covered. Those are the metrics I was referring to in the parent comment.
http://thehealthcareblog.com/blog/2015/03/08/does-the-aca-ac...