First day with a CGM and

I just started my CGM use yesterday and now I can’t figure out WHAT is going on with my blood sugar. I gave myself a correction bolus last night at 11pm. I went to bed at 1am with a reading of 79. Woke up at 7am with a reading of 81 and my graph showed a flat line all night. I tested and it was correct (within 2 points) - so far so good, right? Well, I drank 1 cup of coffee with 2 Tablespoons of half and half, no sweetener. At 8am my reading was 50 points HIGHER. I tested and it was right. Now, I am super confused as to why my blood sugar would have risen after being up and around for an hour and not eating. Any Ideas??

The best information will likely come from your cgm. Simply because everybody is different.

We certainly experience BG rises in the morning due to no external cause. We attribute this to Dawn Phenomenon and have a pre-programmed basal to deal with it.

I hear many people who say that caffeine in coffee causes a rise in BG.

My suggestion for you would be to do the same thing a couple days in a row (granted - hard to EXACTLY replicate a situation) and see what you find. Then tweak things. If possible, skip or delay the coffee. (That would be a very bad idea for my family if I were to do that !!!) See what happens.

I really appreciate our Dexcom G5 cgm. It has provided insight which we never would have otherwise had and certainly has enabled us to have better BG management.


I had not heard that about caffeine, I can skip the coffee without any problem. I certainly would have never caught this, I would have had no reason to check again so quickly after taking the fasting BG. Thanks for that info, I will try it.

Some of us also experience a blood glucose rise that’s linked in time to when we get out of bed. I almost always need to add insulin in the morning to cover whatever happens when I get out of bed, even without food or coffee. I think of it as “when feet-hit-the-floor insulin.”

Your CGM will be a great teacher for you to learn your metabolism. Congrats on laying down a flatline overnight! It’s good practice to always look back to your overnight line. You can learn much by observing and using that observation to try some counteraction, if needed.

Like Terry4, by BG rises about 50 points as soon as I get up. I dont think its too uncommon. Also, caffeine has been shown to raise BG in some people, so that isnt terribly uncommon either (thinking of Barb who bolused for coffee).

Having a CGM will allow you to see more accurately your body responds to things other than food.

I often think it’s not worth putting too much mental energy into working out why in an isolated incident your blood sugar did X. It’s frustrating! However, in my own personal experience sometimes I do everything right, and weird things happen that I just can’t explain.

I try and wait and look for ongoing patterns, if you do the same thing another three times with similar results, then maybe it’s time to start thinking about treatment options (a bolus before your coffee etc.)

As some of the others eluded to, I also need to bolus when I wake up if I am not immediately going to eat food. Otherwise I will find I get a slight increase in my Blood glucose.

So true for me also.

I second @Terry4’s comment. More often than not, my BG goes up after I get out of bed and start my day. It’s entirely dependent upon my activity rather than the time of day, which is why I’m so glad I have a pump because I can deal with it in the moment rather than trying to build it into my basal rate.

Thanks for all the input! I am finding the CGM fascinating. I am a little frustrated that it seems to go along and is very close to BG numbers many times then sometimes it is just WAY off and I have to calibrate. So I am not really sure WHEN my BG is starting to change because it isn’t always showing up. It is going to be hard to see trends if it isn’t showing me the proper information. It says calibration is required every 12 hours but that 3-4 times a day is better but not to calibrate more than 4 times a day. I have done 4 times a day so far because it gets pretty far off. So much to learn and get used to! Thanks again for all the input.

My BG goes up in the morning whether I get out of bed or not. I’ve tested it enough times over the past five years when I get up in the night to have a fair idea of the picture, even though I don’t have a CGM yet. Assuming I didn’t eat a bedtime snack and took my bedtime BG reading at least five hours after dinner bolus, my BG will stay pretty level between bedtime and 4 AM. Then, whether I get up or not, it starts rising. If I go to 10 or 10:30 AM without eating, it will typically be about 50 points higher.

I don’t think it’s the coffee that raised your blood sugar.

I think it’s dawn phenomenon.

I can get up in the morning at 80 after a very stable night, and not eat or have coffee for two hours, then find my bg is now 350, all due to dawn phenomenon.

The diabetes educators and book authors do a decent job teaching you that eating raises your bg, but they often neglect dawn phenomoenon. And all the other reasons your bg can go up even though you have basal and have not eaten.

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What Tim12 said.