I've never had a c-peptide test, so don't know what is involved, or how long it takes to come back?
Have had a self-funded fasting insulin test though. Used thriva.com.
My understanding of a fasting insulin test is that it gives a snapshot of my current insulin level - so is v useful to see if my insulin level is high or low after an overnight fast - which then informs me via the HOMA-IR calculation how much insulin resistance I have.
If I were made of money (actually the test isn't that expensive) it would be very interesting to do the test at different times of day and after different carb and non-carb food intake
Good excuse for a donut, eh?
Which would then enable me to learn whether my insulin resistance before and after 'normal' carb intake was the same as someone without my glucose dysregulation.
Yes, it is a very geeky and number crunchy speculation, but it would be brilliant to know exactly what was happening in response to carb intake. The rise and fall of blood glucose only tells a small part of the story, because I could find that my bg levels stay good on carb intake (because I can pump out lots of insulin but it only barely does the job, which means my IR rises). That would suggest that while I have bg under good control, my insulin resistance is still problematic, with the accompanying raised risk of metabolic syndrome and knock on health risks.
Here is a link to a youtube video where Ivor Cummins shows how undetected insulin resistance is the elephant in the room for many health issues we associate with modern life: