Need fasting BG under 100mg/dl with a C-peptide test

I’m trying to get Medicare approval for a pump.

My endo says I must have my BG under 100 when the c-peptide test is done.

I’m finding that very difficult to accomplish. Fasting for 12 hours doesn’t do it. Taking my morning insulins while continuing a fast doesn’ work. My BG rose and kept rising after a 18 hour colonoscopy prep and similar fasts before fracture surgeries.

I’ve had T1D for +30 years and done ok with GM and MDI. My gross numbers look fine, but the stress fof dealing with increasingly frequent hypo events make me want to switch to a loop system.

I have autonomic neuropathy and gastroparesis. I can have a BG level of 140 mg/dl at 12am and if I don’t go hypo, at 6am my BG can be anywhere from 120 to 200. If I take my morning Novolin R and N and don’t eat that level will rise by 40mg/dl over 3-4 hours. The level of exercize I can handle only has a small temporary effect

My question is:

Do you believe that IM injection of Humuln R can be used to drive down my BG -safely- from 140 to below 100 within 2 hours of taking it while fasting? I have a good safety net, ready transport and the hospital is nearby.

Any advice is appreciated.


Sure, it is possible. But it is easier to go from 120 than it is from 140! :slightly_smiling_face:

If you are only taking your N once a day, and taking it in the morning, it is completely gone by the next morning.

If you want to try some things out, maybe take a small bit of N at night. Like an extra dose, but just a small amount. That would help.

Also, try to test it out for several days before your test is scheduled. Get it dialed in a little bit and adjust it. Don’t wait until the night before the test is schedule.

Do you have a CGM? If you do, you can be a little more aggressive with the N dosing.

But back to your original question, yes an IM injection can bring you down within 2 hours if you take enough. Keep in mind, “more” insulin will bring you down faster, but also farther.

Like for example, maybe 2 units will work, but 4 units will work faster, but might be too much.

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@psfud123 I recall my c-peptide test and don’t recall a requirement for being under 100. Unless you’re absolutely sure of the requirement, you might want to get a confirmation from your Endo/office or the testing site if you trust them. Also, from a practical standpoint, I’ve checked the results of my c-peptide test and they don’t mention what my BG was at the time of the test. Perhaps your Endo is being a very conservative in interpreting the rules to avoid any "Medicare entanglements) and what he/she will sign off on?

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Here is an authoritative statement:

I’ve had doctor’s assistants tell me stuff that I knew was plain wrong; for example recently one insisted that my COVID-19 booster had to be of the same vaccine I had before. She insisted this after I had made my requirements quite clear, having totally ignored them and without disclosing what vaccine she was about to give me. Ignore it.

The CMS also points out that the C-peptide test isn’t necessary, quoting the above link:

  1. who either meet the updated fasting C-peptide testing requirement or are beta cell autoantibody positive;


Levels only need to be documented once in the medical records.

My guess is that testing for the autoimmune antibodies won’t work for you, after 30 years, or, for that matter me (close on 50 years, it will be 53 when I’m obliged to transition to Medicare) but that the C-peptide will be a slam dunk; I can see it would potentially be a problem for a correct diagnosis of LADA and the autoimmune test would be a lot more authoritative.

BTW; I now know that I should get a C-peptide ASAP since I don’t want to get into a situation where I’m stressed trying to qualify for Medicare treatment and have to get a C-peptide at the same time. Useful information!


Is the idea to get your C-peptide level as low as possible?

I’d seen that paper before I asked through MyChart for a pump and CGM to be prescribed if appropriate. I haven’t spoken directly to the endo for more than 6 weeks, just office staff, nurses and educators.

I’d advise anyone in the US over 40 with type 1 of any kind who hasn’t yet been tested, to have their endo order the c-peptide test ASAP.

I’ve never been classified as LADA , that wasn’t a term in the 1970s. My diabetes didn’t come on slowly it happened over a period of 10 days following a bad cold that laid me out. I went to from being healthy and energetic scuba diver with a nornal diet to chugging diet soda and voiding continuously. At admission my BG was +600.


I think Boerenkool is on the right track.

The goal is to get the pump approved. So you want a really low C-peptide test result. If you have any remaining insulin production, a high BG will stimulate your pancreas to produce as much as it can, which could give a higher C-peptide result, and this could make you ineligible for the pump.

So maybe the endo isn’t giving you a rule that the government requires, but rather, a rule that helps you “pass” the C-peptide test.


I think medicare specifically requires bg at same time (for pump approval).


Very similar here; 1972, though slightly slower for me. There was a horrible summer term of running from class to class via the toilets (I was 12) then sitting cross legged on the bus trying to get home. I missed the summer vacation but a couple of years later my parents figured they’d make up for it by taking me on vacation to Kenya. (I later figured out they needed an excuse to spend such a large amount of money.) I was introduced to Scuba the second week, which was spent in a hotel on the beach south of Mombasa. Unfortunately that the guy with the heart problem died while scuba diving and the British Sub-Aqua Club decided diabetics should not dive, so I didn’t get certified until a few years ago after coming to the US.

These days I still go back to MDI for scuba but I do know that the Dexcom G6 survives just fine to at least 30m. The Omnipod Dash pods don’t survive even repeated descent to 25ft (they are only certified for one such descent, and quite frankly that only works when they are full of insulin.)

No beta cells, no c-peptide; there’s a table later in the CMS web page giving actual results. The test requirement is there to establish the second half of the following (in bold):

CSII should be used only in diabetic patients who have been demonstrated to have T1DM or to be insulinopenic.

So the CMS is saying that it will only approve CSII where it is shown that the patient isn’t able to produce enough insulin and one CMS test for this is low C-peptide (the web page gives the justification for this in the table I referred to.) Consequently they will approve CSII for people who are not T1D, including certainly LADA (but then they accept the evidence of the autoimmune antibodies) and people who really are T2, with no antibodies, but have reduced insulin production anyway, I added the bold:

With T2DM, insulin capacity may not be impaired initially. Patients typically have insulin resistance and can produce high levels of endogenous insulin, but the insulin is biologically less effective. The presence of this endogenous insulin permits therapies with various oral agents, which either cause more insulin to be released or improve the effectiveness of available insulin. Over time, however, the beta cells become exhausted, and oral agents become less effective.[9]
This can be documented by decreased C-peptide during the fasted state or after a challenge by glucose, glucagon, Sustacal or a mixed meal.(NCA - Insulin Pump: C-Peptide Levels as a Criterion for Use (CAG-00092R) - Decision Memo)

So the endo wants the lowest BG possible because that reduces natural insulin production and C-peptide along with it. Totally, utterly, irrelevant in your case.

Assume you are injecting long acting such as lantus or levemir? If you are waking up high, then that dosage is too low.

One thing that often happens upon waking, is a liver glucose dump, causing bg rise without even eating.

Agree that a higher BG, with low C-peptide result is indication of lack of insulin from your pancreas. If pancreas was releasing insulin, it would increase c-peptide. (And would keep your bg at lower levels).

First, I’m pretty sure different rules apply if you go on MediCare already on a pump. So sometimes it might be easier if you are considering a pump to get it before? Just a guess as our government at work isn’t always the easiest. My transition to Medicare was easy, but I had had the antibody and C-peptide done in the past.

I know some type 1’s continue to make a small amount of insulin still, Have you had a C-peptide before? Maybe the first years as your beta cells die off there could be a lot of changes, but I would expect your C-peptide wouldn’t change very much as a long term type 1. If you know what level you need to be at, maybe pay for a private test so you know what you are at to see how close you are or that if you already are in the levels required?

This is very confusing I have never heard of having to be under 100 BG. I expect the under 225 is because some might make more insulin to deal with a higher BG level so it gives a false result. I still think that would be more pertinent with someone that actually still makes some insulin and not a long term type 1? I just can’t see it being really pertinent to a type 1, a type 2 yes, but a type 1? Maybe I’m wrong but how could a C-peptide change that much in a type 1 if they really aren’t making insulin or a very tiny amount?

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Thanks guys. I guess I stressed myself out and did a lot of extra work for nothing.

This morning I unexpectedly woke with my BG much lower than its been for a year and dropping. So my wife and I drove to the hospital a mile away, arriving just as the lab was opening.

This hospital is the main site of the medical organization that provides all of my medical care. But as far as they were concerned I was the same as any stranger that walked in off the street

It took 15 minutes for two people to look up the order, print a wrist band and forms for me to sign. None of that is needed at their satellite locations. I told them that my blood sugar was low and dropping. Then I sat in an empty waiting area for 10 minutes worrying whether I’d be called before my BG dropped to a dangerous level.

The blood draw took 3 minutes.

When it was over,I knew my BG was very low and popped 4 glucose tablets to hold me over until we could get home.

I got the test results this afternoon my BG was 57. I’m waiting for the c peptide result.

If I ever have to do a fasting BG again (my doctors haven’t ask for them in more than 10 years) we’ll drive the extra 10 minutes to the satellite location.


Glucagon also stimulates insulin production:

Your endo might consider whether asking people to go hypo to get a low C-peptide actually works…

The doctor said my BG was too low, I’ll need to take the test again. I don’t believe that it will be soon.

Seems to me that a long time ago there was one winter when I could get consistently get through the night, not have nighttime hypo and wake with a “normal” morning level. My A1Cs were in the low 5’s I’m going to see if I can find my old diary. Back when my doctors were literally calling all the shots, I used to record in it whenever changes in my management were made and the results. Also recipes I used to make.

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I suspect everyone on this list is silently (or maybe not) going AAARGGGH. You are not alone, though at moments like this it may seem so.

There’s no requirement that I can see that states a low limit for BG and it wouldn’t really make sense from the CMS point of view, but then the high limit is 225 and that is actually to protect people who might be insulinopenic but do a test with a high BG producing a falsely high C-peptide.

I know that when I face challenges like this I tend to give up, it’s a lot easier for me; why would I care, it’s 20 years down the line, except that is the station the train just pulled in to. I find condensed, distilled, boiled down and bottled righteous anger helps, when released in controlled, directed, ways.

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When I get angry I don’t give up, I try harder or find a way to game the “system”.


Found my old diaries and the time I remembered.

It looks like aside from needing less total insulin, the only thing I was doing differently, was splitting my daily N into 4 equal doses instead of 2 at approx 6 hour intervals. At the time I was working coordinating a project with people in Finland and Calfornia and my sleep was split into two 4 hour periods. I never had a sleep time hypo event during that project. When the project ended I went back to my twice a day N schedule.

DST is this weekend; I’ll need to change my schedule anyway. If I take a slightly longer nap in the afternoon, shots at the 11’s and 5’s is workable. I’m going to try that for the next week, get past the change to DST and see where I’m at.


So control on MDI isn’t good enough to take the test for an insulin pump, but they won’t give you the tools (cgm/pump) proven to improve control?

If you’re really into passing this test and can front the expense, maybe pay for 90 days worth of cgm out of pocket?

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Yes it sounds like “Catch 22”, but I’ve already figured out what to do to get the result the doctor wants.

The problem was not knowing at the time the test was ordered how low my BG had to be and why, plus self-imposed pressure to get the test done ASAP.

I can do it safe and reasonable manner sometine within a week, but the way is not sustainable for me. . With the DST change I’d need to do something similar anyway. For a week I can stick to a very tight clock schedule and more restricted diet than normal, as if I were in a hospital.

The reason I wanted to switch to a pump was to get better control under less tightly controlled condtions.

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