First C-Peptide Test Ever

[Ategeler]

I am scheduled to go have a C-Peptide test mid April. I have requested this through my Endocrinologist. When they called me back to discuss it, they said it was a test they don't offer very often and the nurse wasn't sure what to do about my normal schedule of Levemir. I currently take 4 units in the AM. She told me I should skip my Levemir in the morning and take PM instead. Then eat breakfast in the morning but tell the Lab I fasted so they won't reject the lab sample.

Does this make any sense? I am not sure how the C-Peptide test actually works. And this is the first time I have had to get labs done since taking insulin on a daily basis.

Anyone's input who has experience with this test would be much appreciated!

[lorilei]

I wish I could yell u..havent had a cpeptide since on insulin.....call the lab??

[Ategeler]

Good idea about calling the lab. I may have to try that...

[hardingnerd]

I took a C-pedtide test, grant it I am not on insulin so I can't help you with that. However, they said to eat and then say you fasted?! I didn't need to fast for mine, I am just slightly confused lol. Also wouldn't that also change the results they compare it to?

But most definatly call the lab, they should know the answer.

[Ategeler]

I know it sounds crazy to "lie" to the lab. It seems to me that they need to know whether you are fasting or not-in order to interpret the results appropriately? I think this is going to be a waste of time and money... and on top of it-my fasting glucose isn't going to be accurate either...

[lorilei]

reminder...there are different kinds of cpeptides...for them to provide the appropriate reference range, you need to be accurate about fasting or not...

[mortis505]

Something seems quirky there. Why would they tell you to lie to the lab if they want accurate results? By eating before the test you will be cranking out any residual insulin and C-peptide thereby elevating the levels. Call back and talk to the Doctor about this, not the nurse. Also call the Lab, see what they say about it.

[poodlebone]

I'm not sure about fasting but I am pretty sure that it's okay for you to take your insulin in the morning as usual. C-peptide production has nothing to do with injected insulin. Injecting your Levemir should not skew the test. C-peptide is released only with insulin your pancreas makes. Injecting insulin won't increase c-peptide.

If you eat and your pancrease still produces insulin, it will release insulin along with c-peptide. That will show up on the test. If you fast you'll still be producing some basal insulin and c-peptide but not as much as it would be if the pancrease tried to push out a whole load of insulin at once to cover the food.

I'd say to fast for the test and take your Levemir as usual.

[foxl]

I was told I needn't fast, but since I would be for other tests, that is okay, too.

C-peptide IS interpreted differently, whether you fasted or not. But ... the person who interprets your results and makes decisions based on them would be your MD.

So ... it may be the LAB insists on fasting b/c they follow a "rule book," and that is why your MD advised you to circumvent that. MD may want to know your maximal (ie, non-fasting) insulin release ... ? So I would say, do not second-guess the MD's recommendation!

[Ategeler]

Thanks everyone for your responses. I wasn't able to talk directly to the Dr. but the nurse said she would run it by the MD and see if it was okay to take Levemir in Am and do a fasting test. I think I would trust the results more if I can just fast. Even if it is ultimately based on the interpretation of the MD.

foxl- The nurse confirmed exactly what you are saying about the Cpeptide being interpreted differently. They were definitely concerned about the Lab rejecting the sample b/c their rules state fasting. You may be onto something about the "maximal" insulin release. I am waiting to hear back.

[jps]

I don't believe taking insulin is going to mess with your C-Peptide result. My understanding is that proinsulin is the stored insulin. To become active, it is cleaved - one portion is the active insulin, the other is the c-peptide portion. One insulin molecule yields one c-petide molecule.

Injection of insulin is insulin alone.

So a measurement of c-peptide should tell you exactly how much insulin you are producing.

[lilituc]

I'm not sure about fasting but I am pretty sure that it's okay for you to take your insulin in the morning as usual. C-peptide production has nothing to do with injected insulin. Injecting your Levemir should not skew the test.

Actually, injected insulin suppresses natural insulin production, so yes, it will skew the test. If you produce less of your own (endogenous) insulin, your C-peptide will be lower on the test. Interpret this how you like.

Also, it must be a fasting test, so don't eat before it. There's no agreement on how to interpret non-fasting c-peptide results, and I find it very surprising that they told you to eat.

[Funnygrl]

I'm not sure about fasting but I am pretty sure that it's okay for you to take your insulin in the morning as usual. C-peptide production has nothing to do with injected insulin. Injecting your Levemir should not skew the test. C-peptide is released only with insulin your pancreas makes. Injecting insulin won't increase c-peptide.

That's not completely true. Injected insulin suppresses how much insulin your body naturally makes. If you're supplementing something, your body doesn't have to make as much of it's own. If they want to know how much insulin your body is capable of making (and they don't feel you're at risk of dka), they'll want it done off insulin to maximize natural production.

C-peptide can be fasting or non-fasting, but usually fasting is best because that's what reference ranges are based on generally.

Sometimes there's a "stimulated c-peptide" where a measured glucose load is given to try and provoke natural insulin production.

[foxl]

Actually, injected insulin suppresses natural insulin production, so yes, it will skew the test. If you produce less of your own (endogenous) insulin, your C-peptide will be lower on the test. Interpret this how you like.

Also, it must be a fasting test, so don't eat before it. There's no agreement on how to interpret non-fasting c-peptide results, and I find it very surprising that they told you to eat.

But, I have seen algorithms that permit interpretation of it fasting or non-fasting ... ?

[Ategeler]

Oh My! Lots of information. Well, when the Dr. office called back they said they want me to eat first so that it will stimulate insulin production. She wants to see how much I am producing. I will keep you updated when I get the labs drawn and meet with Doc. I am interested to see how all of this turns out.