I have to get a C-peptide test done in order to get my insulin pump. I am almost positive that I still produce SOME insulin, and it is making me very nervous. My Endo says I am type 1... but I am just curious, because it will help put my mind at ease-
IF I am insulin sensitive (1 unit of insulin can drop my blood glucose 70-100mg/dl, and my IC ratio is 1u:30g... Then I couldn't possibly be producing too much insulin right? I would have to be producing very little insulin because otherwise I'd be type 2 and need more insulin to see the result I currently get?
Help? Reassurance? Any Type 2 using ONLY insulin and VERY small amounts? My TDD is less than 12u.
C-peptide isn't the definitive diagnosis of Type 1, antibodies are. But yes, in general, type 1's have lower c-peptides and type 2's have normal or even high ones. (They are producing lots of insulin but can 't use it well due to IR). But there are definitely ranges in how much insulin even type 1's produce. I believe somewhere there is a chart of average c-peptides for type 1's and type 2's. (Walsh?). But it doesn't necessary follow that if you are insulin sensitive you "can't possibly be producing too much insulin". You could be producing some (still within the type 1 parameters) and as you produce less your insulin use will go up a bit.
Have you had antibody testing?
I believe 10% of T1 can be antibody negative.
My Endo said it could be upwards to 20% of people. She said some people only have antibodies at diagnosis and then don't have them after a period of time. And some people never test positive for them but still produce no insulin or very little insulin.
Because I was Dx Type 2 initially, and no antibody testing was done at that time it's not surprising that I only show trace antibodies 3 years later. She said bottom line, if you HAVE antibodies it is a definitive Type 1 Dx, but if you do NOT, it still doesn't rule it out.
Based on multiple factors- Weight, Insulin Sensitivity, Failure of various oral meds to positively effect my B/G, and then the trace amount of antibodies - that's how I got my Dx.
Also, SOME type 2's also test positive for GAD antibodies- It's rare but it DOES happen.
My I:C ratio is really different from yours... 1:10 to 1:16 depending on the time of day. It seems to just vary from one individual to the next.. depending on a lot of factors.
My c-peptide was 1.1 (low end of normal) when tested, but it was also 2 hours after a meal.
I remember seeing a chart in Walsh's Using Insulin book for average TDD.. and I was at the lower end of the range they listed, so I'm sure you're far below even that. But I wouldn't hang my hat on that being the determining factor just yet..
I hope all goes well this week, I know this has been really long and drawn out for you! I will keep my fingers crossed. :)
A c-peptide is a marker for how much insulin you are producing. A meaningful c-peptide is performed when you have an elevated blood sugar (which would presumably drive an insulin response) and then you either have a low or high c-peptide measurement. This would indicate insulin deficiency or insulin overproduction respectively. The results of the c-peptide only indicate insulin resistance if you have a high reading. This is unlikely given your having already an observed insulin sensitivity.
I am a T2. I had the c-peptide, I think I measured 1.6 ng/mL on a reference scale of 1.4-3 ng/mL. My blood sugar at the time was 130 mg/dL. This basically indicates I am insulin deficient, but says nothing about my resistance. As it turns out, I am insulin resistant. My I:C is 1:4 to 1:10 and I use about 15 units a day just for my bolus. I use an ISF of 20 for corrrection, but I almost never correct. The charts in books like "Using Insulin" are guidelines. As a T2, over 200 lbs, my TDD is within the norms from the book. But if you eat low carb, you will often need more insulin.
Getting a proper diagnosis can be frustrating. I've never had much luck getting the right tests. Getting a c-peptide took 2 years of arguing. In your case, it is extremely unlikely that the results would lead to a change in diagnosis. If you were a T2, you would have observed insulin resistance and required more insulin independent of what state your beta cells are in.
Not necessarily--Your body may still be producing small amounts of insulin that are supplementing the insulin that you're injecting. Some of the new research says that even long time T1s are still producing beta cells and killing them off, so residual insulin production can continue for years. That's one reason the C-peptide isn't considered a definitive test for diagnosing T1.
At dx, when I was in the hospital, my C-peptide was at .3 (of course, I was on IV nuitrition because the DKA made me too sick to eat--my body was majorly stressed) but I recently had a new endo redo a bunch of bloodwork (she wanted to make sure I really was T1)--my new (fasting--go figure) C-peptide was 1.1 (the bottom of normal) but my GAD antibodies were through the roof. Hopefully, I won't have to go through that specific blooddraw again, but you never know . . .
Good luck getting your pump.
Apples and oranges, juliannaegrl; read my comment above and Teowyn's below!
No, an ISF of 100 suggestst that you are insulin sensitivity, which means that it is very unlikely that you would produce "large" amounts of insulin and any c-peptide would also not show "large" results.
I would fight that juliannergrl. The last c-peptide I had was when I lived in Guatemala and though it was below normal, nobody here in this country has tested it. All I needed for my pump approval was an A1C (and it was 6.5, and I didn't hear any of the "that's too good" stuff). So I think these things are individual. I would have your doctor write a note for your insurance as to why it would be good for you to have a pump. The "below normal c-peptide" requirement doesn't even make sense. In addition to being a Type 1 (I assume you got antibody testing which is the definitive diagnosis, not c-peptide) You are insulin sensitive and need low doses which means it's really hard for you to dose accurately with MDI.