The insulin and C-Peptide are usually given when a doc suspect's diabeitis or glucose is high. So it's more then likely your doc didn't ask for it. The GTT (Glucose Tolerance Test) is one that you would remember if you had it because it takes almost a whole day of checking levels after drinking a yuck drink. It's still used but not like it used to be.
So it's easier to push statins then to find the real problem. Anyway here's a Mercola article (long) that kind of says a lot and could very well help in your quest for answers. He dosen't get into the Glut transporters but does get into pushing his products so read it with a grain of salt. It'll give you some ideas.
While looking at Scott taking 20+grams of C and not seeing any results it became apparent to me that the C isn't getting where it needs to go. Encapsulating C in a lipid and not getting into the cells indicates a Glut2 problem which is where insulin comes into play.
I'll let mercola explain it.http://articles.mercola.com/sites/artic ... t-one.aspx
Hope this helps some.
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