C peptide test

Hi @wiserkurtious, good to hear from you again (and good news about your Libre trial! ).
So far as I understand it c-peptide can't be affected by injected insulin as it's a byproduct of natural insulin production from beta cells in the pancreas. It can be either a fasting or non-fasting test, however, so did your consultant tell you which to do?

 

Hi @wiserkurtious so this may be a bit more technical than you want, if so apologies. Basically, endogenous insulin (insulin made by the beta cells in the pancreas) doesn't start out as insulin, it starts out as a molecule called preproinsulin, then proinsulin. A series of cleavage steps happens, with bits getting chopped off until you get the final product, insulin. The C-peptide is one of those bits that gets chopped off (from the c terminal end of the protein, hence its name - biologists seem to be selectively imaginative). Injectable (exogenous) insulin doesn't have all these extra bits to be cleaved off, so there will be no c-peptide from it, so the only c-peptide the test will measure is what your own body is (or is not) producing.

Hope that helps!

 

@wiserkurtious I'd add one thing though. WHile it can't be detected in a test, exogenous insulin does reduce the amount of insulin the body needs to produce, as it reduces glucose levels. If you are doing an unfasted test, I'd expect you to not take insulin to give your body the best possible chance to counter a rising glucose level and produce c-peptides.

I am aware of a friend who also did a fasted C-Peptide test and he was told to disable his pump and wait for six hours before the test, to give the body a change to react to whatever his glucose level was, as injected insulin inhibits this process.

 

You might find this enlightening
https://www.diabetesgenes.org/tests-for-diabetes-subtypes/urine-c-peptide-creatinine-ratio/

 

@EllsKBells I wanted to press 'informative' and 'winner' at the same time but I don't have 2 mice to click! And @tim2000s as well for his explanation to! Brilliant info.