Not sure wear I belong!

I have had some type of diabetes since April 2010. I had GD with my third child that went away after delivery. Fastforward seven years later I was sick with a virus and than became really thirsty all the time. I went to the doctor and bg was elevated so went and had a OGTT done and failed it… Fasting levels are good but don’t handle carbs well at all. I was negative for antibodies and GAD and c peptide was ok. I just had my c peptide levels tested again and since last April they have gone down. I am not on meds and eat low carb and walk at least 2 miles a day. I am often in the low 200’s after eating but will come down on my own within five hours of eating. I am 36 and 5’7 and 117 pounds. could anyone tell me what the signifigance of the falling c peptide levels mean?

Circulating c-peptide is a reflection of the amount of insulin produced by the beta cells of the pancreas. In type 1 diabetes, the beta cells of the pancreas are not functioning properly, the body does not produce insulin and c-peptide levels are low. In type 2 diabetes, the pancreas is able to produce insulin, but the body is insensitive to it. This is insulin resistance. Early in the disease, insulin levels can actually be quite high, since the pancreas responds to high levels of blood glucose by secreting more and more insulin that the body does not respond to. Eventually the continued high blood glucose causes a condition called glucotoxicity, and this adversely affects the beta cells of the pancreas. With time, the body becomes less able to produce insulin, and the beta cell mass (amount of functioning beta cells in the pancreas) decreases. Since the body is less able to produce insulin, c-peptide levels can fall. Generally, the body still does produce some insulin. There is a good correlation between a history of gestational diabetes and the subsequent development of type II diabetes, but certainly not all women who develop GD will go on to develop type II. The absence of antibodies, the dropping c-peptide and the history of gestational diabetes all point to the possibility of type II diabetes, but without knowing your actually fasting blood glucose, your blood glucose 2 hours after mea or your hemoglobin A1c, it is difficult to do other than speculate

I trust the Bill will correct me if I am wrong, but a falling c-peptide may not directly indicate failing beta cells. The glucose at the time of the test greatly affects the interpretation. If you have a fasting glucose in the 200s and your c-peptide is below normal, then you clearly have an insulin deficiency. But according to an accepted model used to estimate beta cell function from c-peptide, the following test both suggest essentially 100% beta cell function

Glucose - 100 mg/dl, c-peptide = 2ng/ml

Glucose - 80 mg/dl, c-peptide = 1 ng/ml

Note that the lab I use (labcorp) has a reference range of 1.1-4 ng/ml, the lower test actually shows a c-peptide below normal. You just don’t need to produce much insulin to lower a blood sugar that is already fine. So a falling c-peptide without knowing your fasting glucose doesn’t mean anything, and even if you have that information, things can go up and down.

Which brings me to one of my unanswered questions, why is the stimulated c-peptide not used to guage remaining beta cell function? Bill, any thoughts?

I can respond in a little more deetail later, but the FDA does use stimulated c-peptide to gauge beta cell function. Measurement of beta cell mass is quite tricky, and some of the techniques used, including imaging, are not fully validated. However, the FDA makes it clear that they want to see an impact of a new drug (for type 1 diabetes) on beta cell function by looking at stimualted c-peptide. They really prefer the mixed-meal tolerance test, using a complex but defiend mixture like Boost, but many practitioners perfer the glucagon-stimulation test. It is a little easier to do, but does have the drawback that it can cause transient nausea. My epxlanation was a little simplistic, because I only want to focus on the basics, and not get lost in the details, but your point is correct - nothing is an aboslute (other than a consistent absence of measurable c-peptide).

Hi Momto3: It certainly appears that you are insulin deficient and that your insulin production is declining (even since April). One thing rarely mentioned in the U.S. but well documented in Europe is that about 10% of Caucasian women develop Type 1 diabetes after gestational diabetes (see my blog on Autoimmune Gestational Diabetes). The British Diabetes Association, Diabetes UK, states, “About five to ten percent of women with GDM develop Type 1 diabetes sometime in their life. These women have a slowly developing form of Type 1 that is ‘unmasked’ during pregnancy.” So there is also a correlation between women developing GDM and the subsequent development of Type 1 diabetes. And, about 10-20% of people with Type 1 diabetes are antibody negative. So don’t rule out the possibility that you have Type 1 diabetes. It may be appropriate to discuss using exogenous insulin with your doctor.