Dexcom: Sudden fake lows at night

Pretty much every night I’ve gotten these sudden spikes lower according to Dexcom. They wake me up with the alarm and get my Tandem ControlIQ to stop delivering insulin, which then leads to getting high and Tandem ControlIQ cranking up the basal and then it happens again where I get these weird fake lows.

When I check my blood sugar after Dexcom tells me I’m at 50, the meter normally says 100. The low is not real, it’s just Dexcom getting weird.

Also, it only happens when I’m sleeping. Pretty much never during the day.

Has anyone ever had this happen? See image attahed!

Dexcom fake low|230x500 .


Looks like it’s a “compression low” which is a term you can search for. Basically, if you sleep with your body weight on the sensor, it tends to squeeze the interstitial fluid out of the tissue around the sensor wire, so there’s no glucose in that area to be sensed. The solutions are either to learn to sleep in another position that doesn’t squeeze the sensor, or when you choose sensor insertion sites, pick areas that won’t bear your body weight when you are sleeping.


Wait until you have a compression low and you are at a higher number, an alarm wakes you, you are half awake guzzle some OJ, then think…but I actually don’t feel like I’m 50 and decide to test and now you are at 200 and headed straight up…It happens! :blush:

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Thanks! This covers it, hadn’t known about compression lows before. I think I will move the sensor off my hip to my stomach where I wasn’t getting these.0


The exact same thing happens to me. It is definitely not a compression low. Almost every morning after 5:00 or 6:00 a.m. I wake up with dexcom telling me I am much lower than my contour next meter. I just got a tandem control IQ and I set an alarm to wake myself up at about 5:30 so I can calibrate and adjust the CGM so it goes up. That’s the only way I can think of to avoid control IQ stopping or reducing my insulin if it’s not that low.

By the way I’m incredibly impressed with control IQ sleep mode. I just got control IQ this Tuesday and already I’m sleeping like a baby. Last night my average glucose during sleep mode was 104 and I had a standard deviation of 5. I used to wake up two or three times a night either drinking juice or giving myself a correction bolus. So far control IQ is incredible.


Completely agree. Even if the only improvement was overnight, it is well worth the upragrade.

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I was hesitant to even go to the G6 but the G6 and the control IQ are great!!!

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Out of interest, what makes you so sure what you get is not a compression low? It’s evident that circumstances other than compression where there is reduced blood flow to the area have exactly the same effect. For instance, when my son has his sensor on his upper arm, often when he sleeps with arms raised above his head he gets “compression lows” even though the sensor isn’t touching anything. Furthermore, while compression lows are usually seen as a sudden rapid drop, in our experience that’s not always the case. When my son is sitting on the lounge and leaning gently on his sensor (either on his arm or backside) I often see a slow downward drift on his Dexcom trace, which bounces back up when he changes position. I’ve also seen the same thing happen due to wind chill (hiking in short sleeves with sensor on upper arm).
These sensors (whether Dexcom, Medtronic or Libre) measure glucose in interstitial fluid by a mechanism in which the glucose around the sensor wire is used up. Accurate readings rely on the interstitial fluid being replenished at a high enough rate for the local drop in glucose concentration (due to glucose used by the sensor) to be insignificant.

I have heard of ‘compression lows’ since Dexcom had their model 7 and 7+ as top of the line. I even heard a Dexcom rep tell this story about compression lows. She was NOT a diabetic and reported she had lows about 3:30 to 4:30 every night for the week she was wearing a Dexcom 7 sensor.

Since she changed jobs, others have said the same thing about lows overnight. The only plausible cause is the compression scenario. I too have had “compression lows”.

The only solution I am aware of is don’t wear/place the sensor where your body will compress the tissue while you sleep. Put it on the other side of your abdomen.


Don’t know about compression lows. By BS do drop drastically at night. My problem laying on the sensor/Tx causes it to stop transmitting. This normally happen when the reciever is on my night stand. I corrected this by putting the reciever under my pillow

Yes… which is why I always test blood glucose to confirm… thanks. great post.

I’ve had my dexcom for about 15 months now. I used to get sudden drops from when I’m sleeping and it clearly was compression lows. I stopped sleeping on my stomach and I never get compression lows. And I don’t move all over the place when I sleep so I know I don’t get compression lows anymore. but my blood sugar does get low at around 5:00 or 6:00 a.m… That’s me and I accept that. Somebody else mentioned that too.

I sleep on my sides so to avoid compression lows 100% of the time, I place sensor inline between belly button and xiphoid process. I solved this problem soon after starting on Dexcom as my BG’s tend to run low to start with so I am hyper prone to compression lows.

I sometimes have “compression lows” without laying on the sensor, but magnitude is never more than 20. I wear the sensor on my stomach and sleep on my back. When I get up sometimes BG goes up very quickly. I think gravity might be the actual cause, Also, I can sometimes see on my CGM graph where I rolled or moved around.

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Has happened to me every night with the G4, G5, and G6.

I just have a different setting for nights (no low alarm) so it only goes off when it thinks I’m at 55.
This is always particularly bad for me the first night of a new sensor, where I sometimes have to turn it off entirely!

I’m hoping they figure out a fix for this like they did with acetaminophen :slight_smile:

I’ve seen compression lows with Dexcom sensors since the Seven series. For me the G6 does seem to be more prone to them. Perhaps the shallower insertion angle?

But for me it depends on the individual sensor (even in the same location) and how long it’s been in place. The problem is more prevalent toward the beginning of a session. It’s a big pain in the rear when it happens- fortunately not that often.

I recently had a case of loss of signal during the night with the receiver next to the bed, and figured it was probably the compression issue. Tonight I had a dramatic false low after dinner and with G6 sensor replaced an hour prior. It showed the dreaded LOW reading where numbers/arrows are not displayed. Meter said 82. First significant discrepancy that I know of after 4 months use.

I want to thank you for your explanation. This has happened to me several times. I will have to change my insertion site to avoid this problem.

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I get this too but it happens both ways - sudden drops (supposedly too low) or sudden rises, repeatedly and only in the time frame of around 3 am to waking. I do not get any noticeable dawn rise (maybe my basal settings negate that).

I think the changes co-incide with sleeping on the side of my buttock on which my sensor is. My finger prick checks regularly confirm the CGSM numbers are not right when that happens.

if the sensor site is getting a little “old”, for that time of morning sleep time, the CSGM screen on the pump screen will show either a series of wave crests or the inverse (rapid fall then slowish taper off), then a break (of no signal) - repeated three or four times. I think that coincides with changing the sides I sleep on.