C-peptide Test Question

I have a doc appt on Monday. I am going to make him do a C-Peptide test since he never has! UGH! My question is this, (I have a call into my doc for instructions, but don’t think he will call back), so do I need to stop taking my metformin and insulin before this test is done, and if so, for how long?

I appreciate all your input. Thanks:)