A1c - why bother?

In December, my nurse practitioner put me on lisinopril and atorvastatin preventatively - my lab work has been great for the past few years but since I’ve been type 1 for almost 30 years, I guess they recommend this as a standard of care.

Unfortunately my blood sugars have been awful this past month and I think it’s due to the atorvastatin. From what I’ve read, it can cause insulin resistance. I stopped taking it (with NP’s permission) a few days ago and my numbers have been back to good.

I have a regular checkup with her next month and for lab work, all she wants is an A1c. I’m surprised they don’t want to monitor my other stats since she just put me on these new meds, so I may get the diabetes panel done anyway.

The point of my post is… what’s the point of just getting an A1c? My Dexcom data is surely more telling. Why is this still the standard of care for people with CGMs??


It’s possibly a useful thing for them to look at.

Her average A1C over X years was this. But after 1 month of atorvastatin, her A1C changed to this


I agree with you, @Eric@allison’s standard metric to now has been a1c, so makes sense to stick with it for common measurement for now. However, I do believe that a1c should be becoming obsolete for those of us using CGM. A 90 day average, if we are on G6 or G7, should be should be an appropriate metric. What the target and range are is maybe a different question (and might vary by person), but the same is probably true for a1c as well (we all have probably have different RBC lifespans). Selfishly, I hate having blood drawn so would prefer movement to a CGM metric. (PS - I just agreed to try lisinopril)


I get that, but I also have 10+ years of CGM data, lab work testing cholesterol, microalbumin, etc. I’d think that would be more useful!


I’ve taken both lisinopril and atorvastatin in the past, but that was before my CGM days! I think I’ll keep the lisinopril for now, but am glad I figured out the statin was causing awful insulin resistance.

Thanks for your thoughts! I agree.


So interesting on the atorvastatin, @Allison. I actually started that about a year ago and I don’t think it messed up my insulin resistance, but I also started taking metformin not too much later and it tremendously goosed up my insulin sensitivity! So they may have been acting at cross purposes (I am now a huge fan of metformin, if we’re throwing new pharmaceuticals into the mix…).

I am going to be pushing for answers to why endos are not moving to CGM analysis vs insisting on CGM blood draws. I also think they are obsolete and an added burden for us.


I was thinking the same thing. I take a low dose (20 mg) of atorvastatin and haven’t noticed any effect on insulin. But then I’ve been taking it so long that maybe there is an effect and I would only find it out if I were to stop taking it.

as far as A1c, for me I like getting these results from two different approaches. So I’m fine with getting my A1c and then comparing it to what the dexcom cgm estimates. It’s a good check.


I do see my A1c as my report card that I’ve gotten for the past 29 years! It is good to compare those results over time, I guess. My goal is under 6 for every draw this year, so I’ll get it checked to keep comparing :slight_smile:

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There is another possible value to A1C’s. This may only be of use to people who are “in the know” about it.

If you see a somewhat drastic drop in your A1C - and everything with your BG management has remained somewhat consistent - the drop in A1C might be because your red blood cell lifespan is not as long as it once was. A shorter lifespan means you have more new ones, and your A1C gives a false low because the new ones are not as glycated as the old ones.

Why is this important? Because shorter red blood cell lifespan can be a possible indicator of other health issues, such as hematological diseases, kidney disease, or anemia.

So the A1C is possibly a good sanity check for other things.


Actually since I donate blood every two months I know that artificially affects my A1c too :flushed:


This is right. Multiple measures that track related but not identical biomarkers are really what you want here, since the cases where they dissociate can be revealing.

My own Dexcom-estimated GMI is always much higher than my lab-derived A1C (like a full point higher in many cases). I presume it’s because of platelet lifespan. I’ve had a few other mildly out of range hematologic results but nothing that has been worth aggressively investigating. And since both of the numbers (A1C and GMI) are sub-5.7% and my time in range is 98% I don’t have great concern at the moment.


My A1c is consistently about a half point below the one calculated by xDrip+ based on my Dexcom G6 readings. If the Dexcom calibration is off a little over time it adds up. And over 90 days you have 9 Dexcom G6 changes where there is no data for the CGM to use. Not to mention the wonky readings on day 1 and sometimes on day 8 to 10. So the A1c is probably more accurate and not dependent on the patient’s skill in managing the CGM. That said, the CGM’s accuracy is probably sufficient for most purposes.


They use different math so the results are different. I see two main factors (both with the G6 and the G7); the Dexcom isn’t particularly reliable below it’s sweet point, which is I think around 120mg/dL(US) and the high BG results are, I think, overstated. That’s just a hypothesis.

HbA1c is immune to systematic sensor errors and, indeed, anything Dexcom might do. It probably depends on the individual too but then so do the Dexcom BG readings.

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I had the same result a few years back, not with the lisonpril (a medicine used to treat heart failure) but just with a statin. I stopped it as soon as I started seeing weird stuff and the weird stuff went away. I’m under massive pressure (wife, endo) to go back on statins so I probably will, but it’s like voting for the other party, yep, once (well, I guess twice.)

My wife was also persuaded to take statins (seems like it’s the new valium) and her cholesterol dropped significantly but her HbA1c seems to have gone up. She’s not a diabetic (she’s a T2, prediabetic; reduced post-prandial insulin response) but her HbA1c is now higher than mine (a couple of decimals, it was a couple below before the statins). All apocryphal of course but scientific experiment is passé.