Overnight lows WITHOUT basal?

So I just did a 1 week trial on a Medtronic CGM. I got the report this morning - seems I went low (<70, lowest was 51) 7/8 nights, usually around 6am but also a couple days it was up and down throughout the night. I’m not taking basal and didn’t bolus anything for meals. Why the lows?

ETA: since I’m posting anyway…any input on why I would also start going low at ~3hr mark after eating when I bolus, even if it seems to be the correct ratio for the food I ate?

have you tried finger-prick testing during those times? Our son often goes low at night on Dexcom but we test and he’s usually in the low 70s to mid 80s. I think it might have to do with what’s going on in his interstitial fluid while he’s asleep

Sometimes Dexcom gives false lows while asleep if you end up putting pressure on it (sleeping on top of it), so I agree re: testing to make sure. Those usually look like a sudden low, in my experience. However, if it’s a slow progression toward low over hours, it’s more likely to be a true low.

If you’re T1, how are you currently treating your diabetes if you’re able to skip basal and boluses? Are you very early stage LADA?

Unfortunately, since it was only a trial, I wasn’t allowed to have a receiver, so I didn’t see the results until this morning (trial ended last Wednesday), so I didn’t check during those times because I had no idea what was going on (and the lows didn’t wake me). It’s definitely a slowly progressing downward trend all night, not just sudden drops. I’ll attach the graph…

@cardamom, ha, that is a LONG story. The short of it is I’m not controlling my blood sugar overall except through diet and bolus when I eat more than lower carb meals. I temporarily experienced normal blood sugars (unless I ate a lot of carbs) after I had my baby almost 3 months ago, but slowly everything’s started getting harder to control through diet alone. I didn’t take any insulin while on the trial because the point of it was to show my doc where I’m at (I was only on insulin during pregnancy, so she hasn’t ever prescribed anything for me, thinking I was still in early stages not needing anything but diet adjustments). Pregnancy kicked things further along, we think.

@Pianoplayer7008, each one of us has a Duration of Insulin Action. For my son, it is 5 hours and 20 minutes +/- 30 mins variability, which means that insulin will act on him for that long. Depending upon the conditions, he may go lower more than 3 hours after bolusing, possibly up to 5 hours after bolusing.

One other factor may be at work – exercise may cause you to go very low, many hours after exercise. Again, for my son, if he has a 2 hour sports practice ending at 5:00pm, if may still be going lower at midnight. This is due to the fact that muscles and liver (and kidney etc.) will be trying to replenish their glycogen supply. They use the sugar present in the blood for that purpose.

If you give more details on your numbers we may be able to be of more help? You seem to be permanently a bit on the low side. Is this possibly a consequence of bad calibration for the Medtronic CGM?

Actually, the graph I posted was just overnight. I’m definitely not that low during the day! :grimacing:

I don’t really exercise much due to a muscle disorder (unless you count breastfeeding a 3 month old and chasing a 2 yr old around exercise), so I don’t think that’s having much of an impact on my numbers.

Welllll, that’s the tricky thing. I can’t really show that I’m having lows because, well, I just can tell by how I feel that I’m dropping and/or dropping too fast, so I treat before I’m actually low (usually treat when I’m around 70 and feeling any hypo symptoms - shaky, weak, nauseated, etc)…here’s an example from dinner recently:

6:00 85BG, 2u
6:20 60 carbs
7:20 71, 18 carbs
7:45 75
8:15 105

And a breakfast recently where I had an initial spike but then dropped relatively quickly despite a snack:

7:45 86BG, 1u
8:00 35 carbs
9:10 173
10:45 6 carb snack
11:20 78, 8 carbs
11:50 107

As I’m looking back at all of this, and with a recent experience eating the same exact meal at the same exact time of day and having different experiences with blood sugar levels/insulin response, I’m wondering if it’s just partially to do with still being in the honeymoon period dealing with a pancreas that’s still spurting out insulin sporadically, making things more unpredictable. I do know that when I don’t take insulin and I spike, I drop pretty fast around the 2 hour mark (unless I ate a lot of fat), so maybe when I do take insulin, my body still responds around the 2 hour mark if I have a decent rise or spike, and that combined with the insulin I injected makes me start dropping low by the 3 hour mark…hm.

I would think being in a period with very low insulin needs would indeed mean you’d see a lot more erratic stuff, since your pancreas/endogenous insulin is probably still in the picture, at least somewhat.

Honestly, this is part of why I went with Dexcom over the Medtronic, because the whole one week blind thing seemed really silly/way less useful than being able to see it as it happened. If you’re considering an integrated pump system, then that’s different I suppose, but otherwise I can’t recommend going with Dexcom enough if you’re thinking CGM, since they don’t do that (and the technology seems better in a number of ways). The necessary blind week seemed so off-puttingly patronizing to me though, like diabetics can’t be trusted with our own information.

We are trying to get insurance to approve a Dexcom for me right now! The Medtronic was mostly just a “diagnostic tool” thing for my doctor. Just another hoop to jump through…my story has been so complicated, I am willing to do just about anything just to have things properly addressed in the end. :frowning_face:

I am sure some of that is true. But, looking at your nightly track, I would still suspect there is something else. You are really low at night on average – not only at one time a time, but overall.

I guess the first thing I would look into is decrease your insulin to carb ratio at dinner (i.e. more carbs for the same amount of insulin). For instance, my son’s insulin to carb ratio is higher at dinner than other meals. This is really the only thing that can drop you at night since you don’t take any basal.

I just noticed you are on UHC. Every plan is different – but I do not a lot of people on UHC on a Dexcom (we are, for instance). So hopefully it won’t be too difficult!

Always take cgm data with a grain of salt, it’s really not that good. That said, you could likely be drifting slightly low without basal due to slowed and prolonged endogenous phase 2 insulin response… the important thing to realize is that without basal insulin though you are highly unlikely to have significant or dangerous hypoglycemia except from the bolus even if you get some quirky numbers from time to time…

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That’s the weird thing - I’m taking insulin for meals, but not for most of my snacks (lower carb), so I usually have a snack before bed that I don’t cover, which I would think would help hold me overnight (and while doing the trial these results came from, I wasn’t taking any insulin at all). One of these nights I’ll remember to take my BG monitor to my bedroom with me and will test around 6am whenever baby wakes me for a few days to see if I’m actually going low. I never have felt low when waking with the baby…

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Ha, so I’m not going to enjoy my CGM as much as I think I will whenever I finally manage to get one? :wink: The number of finger pricks I average seems to shock everyone (in the medical field) who asks me about it.

Cgm is great for monitoring if you bg is generally going up or down and such, learning about your trends etc, but it’s not a precise tool for exact bg measurement

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Ahhh, that makes sense.

Lots of stuff I would agree with Sam on but this one I disagree. We find the Dexcom G5 to be highly accurate and have zero problem doing bolus directly from the CGM readings. When we do our calibrations, the numbers are extremely close. Given the great accuracy, we get better information for a bolus from the CGM as it gives direction of BG movement as well as BG value. We can take the BG direction into account with a bolus.

End of the day, you have to find out for yourself how accurate the CGM is for you. Be careful on how and when you calibrate as doing it at bad times will completely throw the accuracy out the window.

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Also, don’t underestimate the power of knowing what your trend is doing. My teenager has made a number of modifications in his lifestyle because of having access to data. The trend information is very powerful. If it is also close to your actual bg (we find that it is for us) than that is even better.

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I would say this is very much a person-to-person difference. For us, Dexcom is spot-on about 95% of the time – but there are certain specific times it’s off, like when my son is dropping quickly or rising quickly. Still, we are constantly bolusing based on its data, so we don’t have any issues with its accuracy

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Yeah, my experience is that Dex is almost always accurate enough for treatment decisions except that my recovery from lows often happens much faster than Dex reflects, so important to check with my meter if I’m tempted to keep treating (often it’s not necessary). Also if my blood sugars are extreme, I trust the exact Dex levels less (like if it says I’m 342, I’m almost certainly very high, but might be 280 or 390, since the margin of error gets much higher at high blood sugars).


Test with a meter 1 hour post meal and compare to Dexcom-- is it still generally reasonably accurate? Mine is accurate when there’s no noteworthy activity going on, but when bg is on the move I don’t consider it very accurate at all… it tells me if it’s going up or down, spiking beyond target range but I don’t see a whole lot more precision than that… that’s not to say that info isn’t useful… in reality all I really need to know is that my bg is out of range or headed that direction in order to prompt me to take whatever the appropriate action may be… if my cgm alerts at 140 and my meter actually says 200 I don’t consider that very accurate, but it’s still done it’s job and provided its benefit

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