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C peptide tests - fasted or not fasted?

T

T2&confused

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Just that really - should c peptide tests be taken after fasting or not?

I hope this is the right place to ask!

Thanks
 
There are various methods - see here (see table 1) suggest you ask the lab/people doing the test what prep you need to do
 
jonathan183 said:
There are various methods - see here (see table 1) suggest you ask the lab/people doing the test what prep you need to do
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I did, and they told me I didn’t need to fast so I didn’t. And now my results are shown on my record as being fasting glucose and fasting c peptide, which obviously they’re not, hence me trying to understand.
 
T2&confused said:
Thanks for the link. They told me I didn’t need to fast and then took both the c peptide and glucose tests together, so I’m concerned the results aren’t going to be valid ‍
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Fasting can be inconclusive if you have normal fasting blood sugars, you won't be expecting to produce a lot of insulin as your blood sugars aren't spiking. That's why they said non-fasting.
 
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ert said:
Fasting can be inconclusive if you have normal fasting blood sugars, you won't be expecting to produce a lot of insulin as your blood sugars aren't spiking. That's why they said non-fasting.
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I see - thank you for the explanation. Such a confusing and anxious time waiting to find out what’s going on. Thanks again.
 
Recently I had 2 c-peptide tests done, one fasted and one after 3 cups of coffee with milk, everything else the same. The c-peptide on the coffee day was 52% higher.
 
Depends what you want to know. If you need to assess your metabolic health in the setting of existing T2DM, then I think fasting insulin (not c-peptide) is the single most powerful metric. Alternatively, c-peptide (pre and post) is probably a better tool for investigating and diagnosing unclear glucose regulation problems. In either case, interpretation is everything. I definitely wouldn’t trust my GP to understand any of the results.
 
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Not sure if this is weird but my test, I had to eat my biggest meal of the day two hours before the test, I took this as an opportunity to go to McDonald’s and eat a double sausage egg McMuffin, hash brown and latte, followed by English muffin and jam lol did I say that out loud?
 
Jim Lahey said:
Depends what you want to know
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@Jim Lahey, help please, I'm very confused. I suspect I am in an early honeymoon phase of LADA. I'd like to get at any rate nearer to being sure. I will probably have to pay for a private test, so I do want to get the right one, done in the right way. As far as I know only fasting C-peptide tests are available, or I could get an insulin test. Please can you or anyone advise? I don't want to spend £200+ on a useless test.
 
@Alexandra100 sorry but I wouldn’t like to pass comment. My understanding of c-peptide is quite limited and I definitely don’t know much about LADA. Hopefully someone else more knowledgable can help you. I chose fasting insulin but there was no doubt in my mind that I was T2 and simply wanted to know how hot my metabolic fires were burning when supposedly at rest. C-peptide is a different ball game and would surely require more skilled, contextual analysis for the data to be meaningful.
 
Alexandra100 said:
@Speedbird, so no-one discounted your low c-peptide results, saying, "Well, your insulin would be low because you had eaten nothing"?
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My GP, and would not do another test, however my consultant did repeat the test. Also I am not insulin resistant so that probably has to do with my diagnosis.
There has to be a marker either fasted or non fasted. I had 2 c-peptide test, both fasted, 2 years apart, it showed quite a decrease in insulin production on my most recent test.
 
Alexandra100 said:
@Speedbird, so no-one discounted your low c-peptide results, saying, "Well, your insulin would be low because you had eaten nothing"?
Click to expand...

If you/one has any type 2 pathology at all then your insulin levels, at least to begin with, would almost certainly be very high 24/7/365 whether or not you'd eaten, but I don't know how c-peptide would reflect this. It's an indirect measurement and there may be other influencing factors that I'm unaware of.

Worth remembering also that even if insulin production has fallen off a cliff and is now very low, you can simultaneously have serious T2 pathology. This is why insulin dependant type 2 often need increasingly high doses compared to an otherwise metabolically healthy insulin deficient T1 or LADA etc. In other words being insulin deficient doesn't rule out insulin resistant T2DM. I believe the common term is double diabetes. I personally think this is why sometimes diagnoses are so difficult to pin down.
 
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