Why I Set My CGM to Alarm Me at 100mg/dL

Reprinted with permission from DiabetesMine. Read more news & reviews at www.healthline.com/diabetesmine


70-120mg/dL. I think every person with diabetes has had this infamous number range ingrained in their psyche. We are constantly told that anything below 70 is considered a low blood sugar and should be treated. So when I finally got my CGM after seven years of living with type 1 diabetes, I naturally plugged this golden range of numbers into my machine. And I thus commanded my new little black box to alert me anytime my blood sugar dropped below 70.

Fast-forward four years later. I’m finishing up medical school. I’ve studied the human body and gained a better understanding of my disease. And my CGM now warns me if my blood sugar drops below 100. And my diabetes control has never been better. What? Below 100? 100 is considered low?

Allow me to explain. There have been a number of factors that have lead me to make this change:

  1. The CGM lags significantly behind our real blood sugar.* This is because the CGM does not measure glucose in the blood. Rather it measures glucose in the interstitial tissue fluid. You’ll notice it’s not called a “continuous blood glucose monitor” but a “continuous glucose monitor”. The missing word “blood” makes all the difference.(although I’ll admit, CGM has a better ring to it than CBGM).
  2. Another reason the CGM value can lag behind real BG is because it only checks every five minutes. Have you ever done intense, vigorous exercise while wearing a CGM? You’ll be able to watch your BG drop. It might read 130 when you start, then 111 five minutes later, then 96 five minutes after that. Now suppose you whip out your CGM and take a look at it four and a half minutes later. It will still say 96. In reality though, a finger stick at that point in time will probably tell you that you’re already awfully close to the hypoglycemic range.
  3. Lows are horrendous for overall control of BG. When BG’s dip below 70, our bodies alarm us to get some sugar into the system. One way our bodies do that is by releasing hormones that cause us to have intense hunger. (This is why I try to avoid lows when I’m in public – I’ve learned the hard way that people will look at you strangely when you finish an entire box of cereal in one sitting). Throw some clouded thinking into the mix, plus frustration at yourself for your lack of control on your BG, and you’ve got yourself a recipe for disaster. Having the self-control to eat only the required 10-15g of carbs is close to impossible. This knowledge has allowed me to devise The Hypoglycemia Roller Coaster Theorem:

Low BG= Monstrous overeating= high BG = over correcting with angry boluses= roller coaster BG for 24 hours plus. The best solution I’ve found is to simply avoid lows at all costs.

  1. The conventional thinking is that highs are bad in the long term and lows are just bad in the short term. However, a recent growing body of evidence is pointing towards the fact that lows may have some long term effects as well.  You can read about it here.

All this has led me to set my CGM alarm at 100md/dL. This allows me to get the warning well before my blood sugar is actually in the hypoglycemic range. I then have the time to closely monitor where my BG is headed and to prevent a possible low well before it’s too late.

I will throw in one disclaimer: I don’t always have my CGM alarming under 100mg/dL. For example, if I’m going to sleep and my BG is 95mg/dL and I’m pretty certain that it will remain steady, then I’ll drop my alarm down to 85-90 (otherwise my CGM will be beeping unnecessarily all night long).

As CGM technology continues to improve, and CGM’s become more accurate, my hope is that someday I won’t need to have my alarm set at a number that is well above the hypoglycemic cutoff. But until that day comes, you’ll continue to hear me beeping away with a BG of 99mg/dL.


*Note from Dr. Edelman: Some CGM systems have a longer lag time than others. Dexcom is the best at 10 minutes and Medtronic can be quite long. Also remember that CGM alerts should always be individualized.

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    This is pure 100% tomfoolery. A bg target of 100 with a cgm of 100 is not wise. A normal persons blood sugar is 83 so, why would we not strive for the same number? Isn’t normal good? I consume 30 carbohydrates per day and have for the last six years with a high A1c of 5.8 and a low of 4.8. I can post my graph and send you a study conducted by Harvard Medical Research which disproves your theory. I am a juvenile diabetic diagnosed at the age of 18 months. This is my 44th year with no complications. You can call or text me at 256-689-9145 or email me at derekcraulerson@gmail.com. I can send you my graphs, any medical data and information you desire concerning my medical history. My info is listed. #Typeonegrit

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      Hi Derek,

      Thank you for your comment. Different management styles work for different people, and it’s important for everyone to do what works for them.

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    Hi. Good News!! Those of us type one’s that follow Dr. Richard Bernstein’s very low carb diet, tend to keep blood sugars between 70 to l05, with no rise in b.s. after meals. This radical pain in the rear diet is rewarded by blood sugars that can actually be controlled, with A1C’s in the 4’s and 5’s. be . Please see the description of our results in the Journal Pediatrics, May 2018, by Belinda Lennerz.( I set my low alarm at 75, and high at 120. I wish it had high alarm at l05, which is where I may take 1/2 unit of humalog correction.) I have mentioned this regimen to Dr. Edelman once at TCOYD conference, but he was not in favor of it. I challenge you to try it for a month or so. What have you got to loose?? . Check out our face book group called typeonegrit. Best wishes, (for people with proliferative retinopathy, see page 64 in Dr. Bernstei’s book. ; they need to follow their Insulin-like Growth Factor -1 (IGF1) level and go on the diet more gradually.

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    wow. If I set my low alarm at 100 I’d be alarming NON STOP. I feel fantastic even at 85 and rarely go over 120-160 as I really watch my carbs.
    I keep my carbs under 15 grams a meal and none after 6pm which makes spikes and falls less of an issue.

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    So you will Beep Beep Beep a whole lot sooner than I will.
    Beep Beep Beep.
    Many times we do all we can, candy and carb-wise, to make the darn thing stop beeping. So the CGM ends up ruling our lives and we lose control of the CGM.

  5. Although the Dexcom is a great addition to my life, I live in constant annoyance from alarms and more alarms. On top of that is the problem that supposedly interstitial fluid takes longer to recover from lows. So I get a low, I treat it, and then it continues to alarm for 30-45 minutes when my meter shows an in-range BG. If I set my low at 100, I would go crazy within a day. I wish that Dexcom had the feature of muting all alerts for a certain period of time. I used to have that with Medtronic in the SofSensor days. It would actually keep me safer to be able to mute alarms on demand because now I sometimes shutdown the app in the middle of the night when it won’t let me sleep.

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    I am excited to try this suggestion. I have been set at 80 for my low alert and have had a few tough lows lately. I also don’t want endless alarms, so I set to 90.
    My A1c ranges 5.8-6.2, so I am doing well. I don’t want to let DM rule me, but feel I am more motivated than most.

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    I’ve also set the alert for my son’s low alert to 100 and I think that works best for us. It’s only been about 26 months since he was diagnosed so maybe my opinion might change. We were told that staying between 80 and 120 was ideal…and that staying between 80 and 180 was still very good. But we quickly learned that staying between 80 and 120 is, for us, impossible, even for just a 24 hour period. So we’ve pretty much just trying to figure out how to stay between 80 and 180. Setting the low alarm at 100 makes that a lot easier…we bolus to get back to 100 and if his BG level goes a bit lower (i.e., to the low 80’s ) we’re still good!

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      Thanks Edward – we’re glad you found something that works for you and your son!

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    It is not just overeating after a low that throws off the control. The hormonal protection from hypoglycemia can influence the blood sugar to be higher for some time.
    The 100 level for a reasonable low indicator is particularly useful, even protective, for persons who have symptomatic lows. It is nearly required for persons with hypoglycemia unawareness. By preventing lows, the stability of the blood sugar can improve–sometimes even improving the A1c for some.
    I am sure there are true “brittle” diabetics, but I suspect that complete avoidance of hypoglycemia can stop the roller coaster for most. It takes attention to patterns and subtle changes, with care to not treat a higher before meal value following a low episode.
    This discussion is anchored to CGM settings, but applies to all persons with diabetes who have erratic control.

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    I am so glad I read this because I had my low set at 60 and I just realized that I was going down to 40 and because of that I am eating too much and my blood sugar goes afterwards to 200 and I couldn’t figure out why. I think 100 might be a little too much, so I set mine now at 85 and it worked. Thank you so much for helping me with my lows and my highs.

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      Thanks Renate – we’re glad you found something that works for you. That’s the most important thing!

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    I did the trial on the Platinum G4-took my A1C from 8.4 to 6.1 in FIVE WEEKS. Then it ended and I’ve been all over the place. Found that my glucose levels will drop from 80 to 60 in minutes, set alert for 90 and did great. Anyone else who is built small and has a hard time with the Medtronic CGM /pump? By the time I get all the tape on and quit bleeding left no room for rotation.

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      Thanks for sharing your experience. As you suggest, alert setting is an individual thing for sure. We hear all the time about the “stuff” you have to wear with the Medtronic/CGM system. Good luck!

  11. After reading your article, I was Enlighted. I could not wait to raise my limit to 100. I do not sense when my blood sugars are low so I really depend on Dexcom to let me know when I am heading to the danger zone. Unfortunately, I ignored when my alarm at 80 mg/dl I would say to myself oh you still have time and in the next 10 5 min I dropped to 66 and then in 5 min 40 mg/dl. still not feeling the s/sx of hypoglycemia. Of course I stopped what I was doing and took in 30- 60 grams of carbs …. Now with setting my alarm at 100 I can chose to temp turn off my t slim and take in less cars until I above 100 . This is a much better plan for Me. Thanks again

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    I’d like to get everyone’s suggestion on how to resolve the alarm issue with my roommate. He’s diabetic and his alarm goes off every few minutes at random times at night for hours – I’m talking from 9PM til the sun comes up. He’s fast asleep, and I’m losing my sleep and my mind. I’ve communicated this issue with him multiple times and the situation has not changed. I take that the state of his blood glucose may affect his physiology and makes him sleep like a log through his alarm, but it’s really affecting my life too. I’ve tried to be patient but I’m not responsible for his health. At this point, it just seems like he’s being inconsiderate of me and also neglecting his personal care.

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