Doctors Questioning Diagnosis

Hey, all! Been a while since I logged on; life. :sweat_smile:

Is a test of insulin levels at all helpful for someone who has previously been diagnosed with LADA and has been on insulin therapy for several years? Am I correct in assuming insulin tests do not differentiate between exogenous vs endogenous insulin?

Asking because I believe my new doctor (seen today) may be questioning my diagnosis, and I know he’s testing my insulin levels (or at least that’s what he said), and I’m trying to prepare myself for the followup conversation. My rather unconventional diagnosis/initial treatment has led to doctors questioning this in the past, and now it has me wondering if maybe there could be something else going on. :woman_shrugging:


“Insulin levels” do not distinguish between home grown vs injected insulin.

Any doc who even knows the basics of diabetes would be testing your c peptide instead— which is a molecule that shears off of natural endogenous insulin only…. I suspect that is likely what they mean and they are just using layman’s terms. If not I’d have some pointed questions for them

And even the results of c peptide levels can be really hard to interpret

Good to see you


I could be wrong, but I don’t think serum insulin tests are often done as it is a very expensive test. The usual test is not actually testing insulin but C-Peptide. This gives and indication of endocrine insulin secretion. The Beta cells secrete pro insulin which is a molecule of insulin bonded to a molecule of C-Peptide. This gets split. The level of C-peptide then gives an indication of how much insulin was secreted.


Is your treatment working for you? If so, advocate for yourself and don’t fix what isn’t broken.

That’s how I feel, even if some how despite all odds I’m not a type 1, mdi works well for me and keeps me well under a 7% a1c


If you ever had a positive antibody test, it should be clear cut. I believe you had a previous positive test? Get a copy of the positive test of antibodies. My doctor handed copies to me right away and said to keep it, just in case. If your doctor questions the diagnosis, with a past positive test, I would switch doctors. If your doctor is actually ordering an insulin test while you are on insulin, I would switch doctors. But if he ordered a C-peptide, maybe just to see how much you are still making. Hopefully it is just to know where you are in the process, because LADA can take 8 years plus to fully develop. Although it seems a little weird still this many years later. If you have LADA, your pancreas can keep trying for years and per Joslin lots of long time diabetics still make a small amount of insulin.

LADA is completely type 1, it’s just a term that is used when you are older, usually past the age of 30, to describe slow onset type 1, versus when you are younger which usually happens much more rapidly. But there are still doctors out there that are confused about terms, about the time involved, or want to keep thinking everyone is a type 2.


Yes, I did have a previous antibody test, which one doctor told me didn’t guarantee I had LADA since some people “just have antibodies.” That may be true - I haven’t researched it personally - but with my history and other lab results, it seems pretty clear cut to me.

Thank you all for the input. I got my results back (online) and sure enough, he tested my insulin levels, which were high, but also c-peptide, which was 1.6. I’m curious what he’d say to that but with some other concerns and just overall “weird” feeling about this doctor, I don’t think I’m going to go back. :grimacing:


A normal C-peptide range is 0.5 to 2.0 nanograms per milliliter . These levels can be high when your body makes more insulin than usual. Levels are low when your body makes less than it normally should.Nov 7, 2020
C-peptide levels are associated with diabetes type and duration of disease. Specifically a c-peptide level of less than 0.2 nmol/l is associated with a diagnosis of type 1 diabetes mellitus (T1DM).May 8, 2017
I’d probably request another c peptide test to be on the safe side…1.6 is within normal range and many of the type2 injections/drugs may work better… im not sure if its a fasting test, but there might be some odd preparations… ive never heard good things about the antibody tests, all of my endocrinologists swear by the c peptide… i tested in the negative… which at the time my dr. said was rare…

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This is an authoritative second source analysis from 2017:

It answers every question asked so far in this thread on C-Peptide and provides insight on the various antibody tests. The citations (check the link at the top) suggest it is still one of the authorities; multiple citations even so far this year!

Worth reading, start to finish.


After 54yrs TD1, but now over 70yrs old, my insurance, not medicare, wouldn’t approve my new pump without a C-peptide to verify my TD1 status.
It was a box to check for them. Irritated the crap out of me, but as long as they paid for it…
Yea, I’ve been scamming the system for 50+years! If only…


I had a similar case when getting Tandem pump in 2020, with 55 years of T1D. Low C-Peptide had been confirmed as requirement under a previous insurance plan. But new plan in 2020 would not accept that (and i had saved a copy of test result!!). They are just following their rules, but unfortunately wastes our time and money.

Couple more years to Medicare, can’t wait to see if they require the test again to prove I was not miraculously cured.

And to think my pediatrician was able to admit me direct to hospital at my diagnosis, by simply smelling my breath and knowing I had been drinking and peeing more than normal.


Wouldn’t that be glorious, to be found CURED!!


There are many C-peptide tests. From what I understand of them it seems that only GST and MMTT are the only ones that reliably detect lack of beta cells. I suggest ensuring you get a GST (I think we are quite tolerant of glucagon, because, unfortunately, we have to produce it frequently). Timing over an extended period also seems to be important.

Low blood sugar is irrelevant; the insurance company is looking for zero C-peptide, so if you come in with low BG, so what? Where’s the C-peptide? The important thing is to avoid high BG, which suppresses C-peptide in non T1s. Of course we automatically produce high BG in a fast because we continuously produce glucagon, so the trick is to aim for LOW bg and ingest glucose tables (which would produce C-peptide in others) to bring the BG up. Glucose tablets aren’t food, they are medicine, so you did not consume food.

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