Hi there, if it's any help here's my results from the early days when the medics were still scratching their heads about what was going on.
Firstly, the disclaimer: I'm not a medical expert and please do not take my information below as diagnosis for your own condition.
My c-pep was 0.46 vs range of 0.36 -1.16, at the time I was told I was in normal range....so they went off to do some fancy genetic tests for MODY instead (both my parents are T2 so even though I didn't fit the typical T2 criteria, the medics just followed the genetic route...I was negative for 2 of the common MODY types)
About 6 months from that c-peptide result I was then tested for antibodies by an Anti-GAD test, as I was low carbing but my glucose readings would reach mid to high teens, sometimes in the 20s. I just felt iller and iller and people around me were commenting that I looked tired and losing weight. I was peeing/drinking water (but I was doing that for ages and just thought that was just part of me!).
The Anti-GAD was positive and I'm LADA/T1.5.
I think based on my initial c-pep being closer to the lower end than the middle, they could have save some money by doing an Anti-GAD then or I suppose in my case, it was a case of waiting for things to get a bit worse before a clearer diagnosis.
Anyway, so far based on my results, your C-pep is outwith the range. i.e your insulin production is low.
I don't know how they will test you for insulin seperately - I thought the c-pep WAS the insulin test.
I would suggest you ask for an Anti-GAD too. Although not all show positive for antibodies, it should be done along with a c-pep to determine if the Diabetes is autoimmune i.e T1 / T1.5 etc
Good luck.