C-peptide is what you see to see your insulin levels, just cheaper than insulin testing isn't it? I'm away from home so don't have my computations on it around. But I did sit down with a c-peptide result and try and work out online what that meant in terms of how much insulin I was producing. I think I worked it out that I was in the normal to high range of insulin production - which means I have a really big whack of insulin resistance. It is good to know, so you can work out a good management/treatment scheme that is right for you. (There is a big range of how T2 is expressed. And it can make a big difference to how you can get better with it.)
