Interpreting Low C peptide with other normal results

Hi everyone

First time posting here and I hope I’m in the right place and not overstepping any boundaries.

I will try to keep this simple as it involves a history spanning the last couple of years. Over the past 3 years my fasting blood sugar has been hovering between 88-115 (just recently was 115 last month during a routine physical but I was very stressed out the evening before and morning of regarding a different matter so I’m not sure if my stress levels reflected in my blood sugar. Previously it was never this high, highest was 103). My a1c has ranged between 5.5-5.7 (mostly always 5.5). I am on a statin for a family history of high cholesterol and heart disease but my lipid panels are totally optimal. I go every 6 months to my cardiologist for routine blood work and that’s why I am always exposed to my blood sugar ranges.

Technically Based on the above numbers I am prediabetic. I am 5’11 180lbs and can lose some more weight from my midsection but I’m not out of shape. Three years ago when I first got a reading above 100 I weighed 230lbs and gradually took up exercise and gradually lowered my carbs until I’ve reached a point where I eat a low carb diet (can’t say strictly keto)

Long story short I’ve been trying to get to the bottom as to why on occasion my fasting blood glucose sometimes tops 100and my a1c although no diabetic fringes on almost prediabetic (with once instance prediabetic at 5.7 a couple of years back). I bought myself a glucose meter and noticed 1) my blood sugar goes up after exercise and hangs out there for like 2 hours or so in the 110 range and 2) my blood sugar after meals are always optimal (never tested after a carb heavy meal because I don’t eat carb heavy meals except when on vacation)

My cardiologist suggested I go see an Endo to curb my curiousity/concern and I have an appointment scheduled for next week. In advance of our consultation she ordered blood work for me which I took and everything came back within normal limits except for the c peptide which was literally a tick below normal at 0.79 (normal range is 0.8-3.4). I fasted at least 10 hours before that test and the day before only at one meal (I do a lot of intermittent fasting). My fasting insulin was 4.4 and my fasting glucose was 88. My a1c was as usual 5.5.

I want to assume that the low c peptide is a product of my low carb eating and intermittent fasting and hopefully not an early indicator that I am developing LADA. Unfortunately no antibody testings were ordered so I have no clue about autoimmune possible issues. I’m trying to figure out if I’m truly no diabetic or if I’m just very well controlled and of course rule out the slim possibility of LADA. Any insight would be appreciated in preparation of my upcoming consultation

I would request that the endo order some autoimmunity antibody tests. There are several autoimmune antibodies that can be tested. One of our members, @Melitta, has written extensively on this topic and you can discover her writing by using the TuD search tool.

Here’s one of her topics.

Your c-peptide test could very well mean early stage LADA, so getting the autoimmunity tests are important to confirm. I think you’re smart to implement a low carb way of eating. That takes pressure off of your pancreas. But a lowish c-peptide and an A1c on the low border of “pre-diabetes” are significant. Low c-peptide is not related to low carb eating. It is a measurement of how much insulin your body currently produces.

I am not a doctor but I think you deserve a credible explanation as to why these two tests are at these levels. Unfortunately, doctors often miss this diagnosis.

Congrats on proactively getting and using a blood glucose meter. Writing down some of your results and providing context (B4 breakfast, after exercise, after a meal, before bed) will give the endo more data to consider.

Good luck with your endo appointment. Please share what you learn at that visit.


Here’s a more recent thread by @Melitta.

By the way, welcome to TuD, Dre!


Thanks for the response and kind words.

I’m actually very aware of LADA as my good friend’s sister developed it just a couple of years ago in her late 30s. In all honesty, it’s because of my understanding of LADA that I scheduled a consultation with an Endo despite my cardiologist telling me not to worry and I’ll be fine and we’ll see how things play out (I see a cardiologist for preventative reasons as I believe I mentioned earlier). We initially thought that the previous statin I was on (Lipitor) was causing the increase in my blood glucose as it is a known side affect. He switched me to another statin (Livalo) and my fasting blood sugar dropped down to the mid 90s for a year until my last blood test last month that showed my fasting glucose to be 115 (again I was ultra stressed the night before and morning of).

I’m trying to be level headed about things and although I do realize that the possibility of LADA exists, I think logically speaking low c peptide in the presence of normal insulin and fasting blood glucose and A1c can be interpreted as my body just not needing to make that much insulin to control my sugar. That’s why I figured my low carb diet and fasting may be contributing to this lower c peptide number. But logic I guess doesn’t always go hand in hand with clinical medicine and hence my appointment this week with an endo to get to the bottom of things. Has anyone experienced similar situation?

Sorry @Dre , But as @Terry4 says you need to get the antibody tests done. There are several, although GAD is the most popular as it’s the one most have a positive result on. But sometimes you can be negative on GAD and positive on another or you can be negative on all of them but end up losing the ability to make insulin and they don’t know why.

Change of diet, medications will work for a while for a Type 1/LADA because you still make insulin for quite a while as an adult onset type 1 (years). That will slowly stop and your numbers slowly go up.

I caught my first numbers going up when all of a sudden I tested at 115 and 117 in the morning fasting. I had always been between 100-103. I had gotten a monitor because an uncle had had type 1 and it sounded like a good idea and I would test every few months. The first couple of years I was told don’t worry about it, it’s just fluctuations as my A1c climbed from a 5.3 to 5.9. My GP at the time and an endo said you’re prediabetic and then a type 2…and they never tested me for type 1. I honestly think it’s because I was overweight, not obese, but overweight they just assumed I was a type 2. Even when I asked several times if I could be a type 1 as I had an uncle that had been a type 1. I swam 75 laps in a gym pool 5 days a week, had a very healthy diet and it didn’t make sense to me. It wasn’t until I switched doctors that the new doctor sent me to a new endo and then she tested me automatically without me even asking and I was diagnosed right.

I’m just telling you this because doctors even now ignore signs of type 1/LADA in adults. If it’s caught early especially with numbers that are borderline they just brush it off as having blood sugar issues as prediabtetic or type 2.

So be pushy about finding out. It’s better to know than ignore the possibility. C-peptide measures the insulin you make. The trick here is low or low normal is a sign of type 1, as you are lacking normal insulin production. As a type 2 or even prediabetic your numbers will be high normal or high as your body makes extra insulin trying to cope with the inability to use what you have properly.

But I’m not saying you are, there are all sorts of reasons lab tests have off readings, there is always a range of percentage things can be "off: Your numbers aren’t even off by very much. So it’s not necessarily a sign of anything, who knows with our bodies sometimes? Stress, yes, medications, especially cholesterol medications have been known to raise BG levels. Your c-peptide is normal enough that it’s as close as it can be to normal?

But the best thing to do is to be tested for the antibodies. That would help one way or another with some answers.


By all means see an endo, though it would have been easier for your Dr to include antibody for your peace of mind. I see nothing wrong with your numbers. If you were heading to T2. I would expect a rise in c-pep and fasting insulin. With LADA I would expect higher BG with lower c-pep, fasting insulin. A 10hr fast BG of 88 with 0.79 c-pep, fasting insulin 4.4 (2 to 20 mIU/mL) all sounds fine to me. I don’t see anything that would indicate further testing and an antibody test.
I’d spend the money and time on a hobby.

For peace of mind, I would first retest that which is causing your concern. You believe your stress levels may have affected the test then definitely give it another look.

1 Like

So I did get retested about 5 weeks later and my fasting blood glucose came back at 88 (this is btw after eliminating fruits from my diet…I was eating a lot of fruit prior to that). That same blood test revealed the fasting insulin to be 4.4 which is great but my c-peptide at .79 just out of normal range. Again, I understand that lab values are dynamic and should be viewed on a spectrum that’s why I’m not losing sleep over it. I just feel my blood sugar health is in this gray area where the values teeter-tot between normal and just slightly out of normal.

I’m trying to find out if that’s just how my metabolism is set or are these hints for me being on the very part of the diabetic spectrum. My dad who is 75 with a history of some heart disease (no diabetes in my parents but I do have two type 2 uncles who could benefit from lifestyle changes) claims he’s been in the prediabetic range his whole life and that’s how his body is just set and may be the same for me.

I complicate matters however by choosing a very low carb way of eating and do intermittent fasting regularly (typically 16/8 and once or twice a week a 20 hour fast). I know this would change the dynamic of my biochemistry and can possibly mask issues (ie am I healthy or am I just really well controlled). That’s part of the reason I’m not jumping the gun on LADA because I’m fairly certain my diet is playing a role in lowering my fasting c peptide but I agree with other posters I will request the antibody tests to rule out the LADA, there is no reason not to.

This diabetes stuff is way more complex than I thought.


If you want to get clear results from those tests, you will need to do it while fasting 12 hours.
And then repeat the test when you are not fasting at 2 hours post meal.

However like a few people have already suggested, an antibody test could clear up the whole thing.

Some doctors will tell you, hey group got got type 2 so , you don’t need the test, but if it were me, I would insist on it.

It doesn’t really matter that much. A lot of the lifestyle changes will be similar, but your treatment will be different.

There are several type 2 diabetic drugs taht warn type 1 people from taking. Knowing what the deal is will help you

1 Like

I think. You don’t need to concern yourself. Every test you’ve had is normal and wouldn’t indicate any need for further testing. Nothing in your tests indicate anything near diabetes.
I doubt this is the first concern you have had. If anything I would talk with someone about why you have concerns on different things.

@jack16 That’s being unfair. When you know something is wrong, sometimes, in fact a lot of the time, there is something usually wrong. He/she has had a change in numbers and is curious about what is going on. Maybe it’s nothing, maybe it’s not.

Medical can be lacking given that they sometimes have very little time to explore small changes. There have been many occasions in the past where only repeated asking and visits led to the proper diagnosis, a fracture, a torn cartilage, a year to find out there was a cancer diagnosis that luckily turned out not to be cancer when more tests were finally done.

So if he/she wants to explore the why of it, more power to him/her.

Unfair would be stating it’s a mental health problem, because I can only guess. There is nothing wrong with the 2 blood tests 5 weeks apart. There is nothing to indicate to have a third. From the tests there is nothing to explore. Do you really think this will end with an antibody test? Will we test for pancreatitis or a pancreatic cancer too? Perhaps a full PET body scan?

It’s funny you say that. I was diagnosed at 21, and I was having hypo reactive episodes because my islets were still functioning.

I was tested for pancreatic cancer at the time. I also had a c peptide test. And insulin levels .

They told me I was too old for type 1 which is why they did all that testing, even though I was very underweight.

So finally an endo made the call and I got some insulin. I felt a ton better almost immediately.

So what I’m saying is, that sometimes it’s not obvious what is happening. An antibody test doesn’t cost that much and LADA is often misdiagnosed as type 2.


You had symptoms warranting investigation and were one of the 10% of T2 who are misdiagnosed. As RH T2. With the OP, there is nothing. I would go further and say it would be malpractice to run an antibody test for the insurance to pay. As it would be to do a PET body scan.

I will add that it sounds like you didn’t have an antibody test? And had a successful outcome. Not that I would suggest it wasn’t needed in your case.

I was pretty obviously type 1, but my reactive hypo made them second guess it.
I was diagnosed in 1987 and the antibody tests didn’t exist.
But they did a nose swab on me and found coxsackie b virus which is a very common trigger for type 1.
I think they did every test that was available at the time.
Then I started insulin the same day.

I had antibody tests done years later because I developed a second autoimmune disease. I had high levels for all 3 antibodies, which I expected but my doctor wanted to know which ones so he could treat me the right way

1 Like

It still took a good doctor to put the pieces together for you. With misdiagnosed T2. They can just progress onto insulin when their BG gets too high on non-insulin meds. The 10% misdiagnosed is probably higher.

There is nothing to investigate for any diabetes with the OP, as the the 2 tests and the doctor said. This coming appointment with the endo will likely confirm the same. I think best practice would be a referral to counseling.

So I totally get it to why you’re coming to this conclusion. Just to clarify, I know I am not currently diabetic because of my numbers. I think you’re missing the goal of what I’m trying to pursue in this consultation.

According to a lot of people (granted not all clinicians), there is no such thing as prediabetes and once your numbers hit the prediabetic range you are essentially on the diabetic spectrum. Meaning, your body for whatever reason can’t handle carbs etc. according to my historical numbers I am clearly prediabetic (fasting blood glucose over the last 3+ years range from 88-103 with the one exception of 115 which I think was stress induced). Now all I want to know from a seasoned clinician is if I am indeed showing some kind of biochemical impairment or is this just where my inherent biochemical metabolism is with no impairment (I plan to provide the endo more info than just my fasting blood sugar and recent A1c to make that determination. Now I fully don’t expect the endo to tell me I am diabetic but i do want to get a better understanding on where things stand because if based on his clinical experience he feels I indeed may be showing early signs than I want to know what type I may be (I personally think IF there is predisposition to impairment I am a type 2 based on my BMI which is a hair over 25 and midsection visceral fat that I am SLOWLY melting away over the past 2 years in addition to family history of two uncles who r type 2 non-insulin dependent). The c peptide I understand in the grand scheme of things will be considered normal based on my diet and numbers. However I am not a seasoned clinician and I am not going to go by my own research and logic. I’d like to know where things stand because if there is indeed early signs of impairment I’d like to be able to quell them now before it becomes much more difficult later should things take a turn (assuming there is no LADA involvement and I am assuming there won’t be based on my historical bloodwork and also my own blood glucose monitor).

This is not anxiety this is taking pro activity in my health so I can maintain good quality of life if the opportunity is there

I also keep forgetting to mention I want my thyroid checked. The past two winters my hands and feet have been freezing and I’ve been diagnosed with primary Raynaud’s in my feet (not classic but all other vascular issues ruled out). Wondering if thyroid is playing a role in my blood sugar control in addition to effects from my statin

Apologies if I or others here are pointing this out, but most of us here would LOVE to have numbers like yours.

But it’s also possible that you are eating and exercising so healthily that you are indeed hiding the onset of LADA through hard work.

It’s a gnarly test, and I wouldn’t push for it if it was me!, but a glucose tolerance test might give some bg curves that would help pin down what if anything is going on. You describe your bg response after several classes of events and there’s nothing obvious that this might prove. Except that typical carb load in a glucose tolerance test would be a much bigger than your current low-carb diet, to see how your bg responds.

I think you are exactly right, eating low carb can result in lower insulin needs which will result in lower C-Peptide labs than typical population.

Your A1C is higher than would be expected based just on your self-tested bg’s. But not enormously so. That could be some testing variation, or is it possibly elevated A1C is mostly because you’re a high glycator? More on high glycators in an academic sense (but which may not help you other than let you know there can be real measurable variation in glycation among those with similar bg’s):

1 Like

You maybe be too early in the disease progression for it to show. Not sure your doctor would be willing to do this but ask for a Glycimark test to see if you have post meal spikes that may get averaged out and not be reflected in your A1C or fasting level.