c-Peptide test and IR

reefedjib · #1 (**permalink**) 08-08-2009, 10:34 PM

I thought of another question. I asked my doc to give me the c-Peptide test and she said no. What I am wondering is if the c-Peptide test, along with my TDD and BG numbers can give me some idea of how much IR I am exhibiting. Is there another way to measure IR? I still want the c-Peptide test, as I am a data hound - the scientist in me.

foxl · #2 (**permalink**) 08-09-2009, 07:39 AM

Rob, I can answer that one from my survey of current literature ... you won't like it though.

There are experimental method of measuring IR, but no clinically approved methods. Two test names come to mind HOMA-IR and Quiki or Qwiki IR (sp). I do not know what they entail but they sound inconvenient and still-theoretical. You might google them and see what you make of the results ...

My reaction was "shrug."

Did you ask your MD WHY no C-peptide? My MD was willing to do a C-pep but not autoantibodies, until I pushed. Also is this an Internist, or an Endo? Endos have a better working knowledge of C-pep and how to interpret the results, usually.

I think we have discussed the decision-making issues here on C-pep -- fasting vs. fed, vs. random, etc. And half-life of C-pep being still quite brief, it is merely a snapshot, like a fasting blood glucose ...

Hope this all helps, my coffee is a-hummin'!

Funnygrl · #3 (**permalink**) 08-09-2009, 08:21 AM

You can ask for a total serum insulin level test. If your total serum insulin is below a certain level with a normal BG you're not considered insulin resistant. Total serum insulin would include naturally produced and injected insulin.

foxl · #4 (**permalink**) 08-09-2009, 08:29 AM

Quote:

Originally Posted by Funnygrl

You can ask for a total serum insulin level test. If your total serum insulin is below a certain level with a normal BG you're not considered insulin resistant. Total serum insulin would include naturally produced and injected insulin.

True, but c-peptide is the more commonly used b/c it has a longer half-life in the blood than insulin ... both are a matter of minutes!

reefedjib · #5 (**permalink**) 08-09-2009, 08:50 AM

Quote:

Originally Posted by foxl

Rob, I can answer that one from my survey of current literature ... you won't like it though.

There are experimental method of measuring IR, but no clinically approved methods. Two test names come to mind HOMA-IR and Quiki or Qwiki IR (sp). I do not know what they entail but they sound inconvenient and still-theoretical. You might google them and see what you make of the results ...

My reaction was "shrug."

You're smart! I found a little literature on both of those (QUICKI), and my reaction is similar to yours...*shrug*. All very statistical with reference to the fasting insulin and glucose clamp determinations of insulin sensitivity. I suppose we could roughly measure IR experimentally. If a Type 1 tells us their insulin needs, with similar carb factors and correction factors, then a Type 2 could seee that they take say 60% more insulin, so IR would be 60%. YMMV.

Quote:

Originally Posted by foxl

Did you ask your MD WHY no C-peptide? My MD was willing to do a C-pep but not autoantibodies, until I pushed. Also is this an Internist, or an Endo? Endos have a better working knowledge of C-pep and how to interpret the results, usually.

I think we have discussed the decision-making issues here on C-pep -- fasting vs. fed, vs. random, etc. And half-life of C-pep being still quite brief, it is merely a snapshot, like a fasting blood glucose ...

C-peptide is the test I really want to see the results of. I don't think it is that expensive, but perhaps it is. As high as my basal dose has gone (76 units), I figure I have a mixture of insulin defeciency and IR. I'd like to get a sense of where it is.

Quote:

Originally Posted by foxl

Hope this all helps, my coffee is a-hummin'!

Enjoy it! I had mine at 7:30 this morning. Thanks for your answers.

foxl · #6 (**permalink**) 08-09-2009, 09:04 AM

Happy to help!

Not much point having found all this stuff, and not sharing it!

Funnygrl · #7 (**permalink**) 08-09-2009, 11:57 AM

Quote:

Originally Posted by foxl

True, but c-peptide is the more commonly used b/c it has a longer half-life in the blood than insulin ... both are a matter of minutes!

C-peptide won't give you any idea what kind of effect the insulin you're injecting, has, though. You could have a high c-peptide and not be insulin resistant at all if your glucose is low and you're not injecting any insulin. However, if your c-peptide is high, you're injecting 100 units on top of that, and your glucose is 70, you still probably are insulin resistant. Likewise, you could still be insulin resistant with a c-peptide of 0 if your total insulin level is high and your glucose is still high. You really need the whole picture.

Tribbles · #8 (**permalink**) 08-09-2009, 01:04 PM

Quote:

Originally Posted by reefedjib

C-peptide is the test I really want to see the results of. I don't think it is that expensive, but perhaps it is.

It's $100 based on a bill I just got sent (insurance screw up, need I say more?) which seems to be a bargain compared to the Vitamin D test at $150.