What is a good standard deviation when using a CGM?

For many years I hadn’t used my Dexcom CGM except for when I went away for periods of time, and usually I paid little attention to the overall statistics as I;d often be travelling and the levels were outside of my normal expectations for a large number of reasons. After some discussions with my Endocrinologist and CDE I’ve now been running one in my standard day to day life for the past few months.

I’m wondering what is the standard deviation people aim for? Currently I’m running 1.5 standard deviation, with 85% of my time in range, 7% below and 8 % above. That’s from my 30 day report at least, it obviously fluctuates from week to week.

I’ve set an arbitrary goals for myself to be running 90% of the time in range, standard deviation of 1.3 or less, 6% above and 4% below range.

I’m struggling at the moment to hit that.

What do other people aim for? Is there a generally accepted goal within the community?

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@Donman90 - I target a Standard Deviation of less than 1.0 mmol/L with a time in range (TIR) of 95% or better.

Sometimes I hit home runs and see 100% TIR

My low & high thresholds are set at 3.4 & 7.0 mmol/L (61-126 mg/dl), and my target BG is 4.6 (83 mg/dl)

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Thanks @Jim_in_Calgary. That’s an impressive chart! Currently my low rate is 3.9 and my high rate is 8.0. My goal is 5.0. Are you on a low-carbohydrate diet?

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Thanks @Donman90

I am low carb (under 20 grams / day).

Being in ketosis enables me to run lower BG levels than I ever thought possible (without the usual diminished cognitive function we usually experience)


I look at it differently. I start from where I am. Am I having too many high or lows that cause me to disrupt my day to make adjustment ?

Each person has a range that’s best for them and their circumstances.

I found my “sweet spot” on CGM to be alerted at 70 and 140. This lets me decide if action is needed, not necessarily that I’m out of range.

If your A1C is in higher range, than tracking std deviation may be more helpful to access spread and areas to focus on.

I just check time in range on Clarity.

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When I started following my standard deviation several years ago, I targeted <= 1.7 mmol/L (30 mg/dL). I read one study that concluded that the 14-day report was a good period to use. It stated that 14 days provided good data sufficiency while still sensitive enough to reveal the parts of the day that need work. This was the study that coined the term, “ambulatory glucose profile.”

I believe that glucose variability is a key metric for monitoring glucose exposure. When it is low enough, it permits targeting a lower blood glucose average safely. One mistake people make is trying to lower their glucose average without keeping an eye on glucose variability as indicated by the standard deviation.

Aiming for a lower average without lowering the standard deviation sets one up for undue hypoglycemia risk. This is what most doctors worry about. They seem to assume that all their patients experience high variability and so jump to a hasty conclusion that a low glucose average equals a high hypo risk.

Using a low carb way of eating (< 30 grams/day) and an automated insulin dosing system, I’m able to keep my standard deviation in the range of 1.0-1.4 mmol/L (18-25 mg/dL). For the last two weeks, however, I’ve relaxed my discipline since I’m on a European holiday. My standard deviation has slipped to 1.8 mmol/L or 33 mg/dL. I’m flying home today and I’m confident I’ll be able to restore my control to former levels.

I measure my time in range performance using 3.6-6.7 mmol/L or 65-120 mg/dL and usually can meet that 80-92% of the time. The clinical standard for time in range is usually set to 3.9-10.0 mmol/L or 70-180 mg/dL. While this standard is suited for a broad range of the patient population, I use the tighter range because I can often meet it and I believe that extended time in the 7.8-10.0 mmol/L (140-180 mg/dL) range is less healthy.


The reason why my endocrinologist and CDE managed to convince me to go to the CGM was actually this. For the past 3 years I’ve had Hba1c consistently below 5.6, with most of them being around 5.2-5.4. This originally started with following a very low carbohydrate diet, but for a number of reasons I couldn’t keep this up. So I moved to a moderate diet, at about 100-150 grams per day but mostly from vegetables and starchy carbohydrates.

However, I’ve struggled over that period with probably too many instances of hypoglycemia, and also I’ve had issues with this and in general just waking up to check my blood sugar. So I really got the CGM to try and resolve a few things; reduce my overall time spent in hypoglycemia and try and reduce the disruptions to my sleep caused by diabetes.

It’s only been a month, but so far for the later it’s certainly working. I still would like to see my overall time in hypoglycemia drop though.



Out of curiosity what kind of bolus insulin are you using (basal insulin as well if you’re not on a pump)?

Perhaps it’s time to try something a bit different to see if you can dose for those starchy carbs without the resultant lows?

Do they sell Afrezza in Australia? I switched from Humalog to FiASP a couple of months ago and I don’t think I’ll ever go back (no Afrezza in Canada :canada: yet).

For me, TIR is directly related to my carb intake. For everyone, the TIR as reported by the software is also dependent on how tight you make the upper and lower limits. My upper limit is 150. My SD is always greater than I’d like it to be. :slight_smile:

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Currently I’m on novorapid as my Bolus, and levemir as my Basal. I am very strongly considering trying a pump in the next few months. I’d love to try Afrezza but currently it’s not sold in Australia, you can get it via some relatively expensive routes I think?

I’m tempted to trial the pump as I’ve seen some people do some cool things with their basal dosages on the pump, and it might give me some more flexibility there.

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If you are an active person there’s nothing better than being on a pump because of exactly what you mentioned–flexibility. The ability to suspend or reduce basals for periods of activity is a remarkably freeing experience. You’ll love it if you like activity!

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Here is interesting article on time in range


By scanning more frequently, people are viewing their blood sugar data in real-time more often, allowing them to make the adjustments needed to avoid highs and lows, whether that’s introducing a new habit or working to change a longstanding behavior.

4 Scans/Day (Lowest) 10 Scans/Day (Median) 40 Scans/Day (Highest)
Time-in-Range (70-180 mg/dl) 48%

(11.7 hours/day)|56%

(13.5 hours/day)|70%

(16.9 hours/day)|
|Estimated A1C|8.2%|7.5%|6.7%|

It’s crucial to have the food, exercise, sleep, and mindset tools to make changes based on your CGM data . For diabetes habits that can be hard to change, Adam swears by modifying your environment, starting small, and reframing long-term incentives as short-term benefits


Thanks Dave, that’s good to hear. I’m definitely active to a degree, I go rock climbing and ride my bike to work and university, and try and do weights twice a week. I’ve read some cool approaches around increasing your basal rate before a weights session to mitigate the rise in blood sugar that often comes from anaerobic excericse. Currently I just give a bolus, which more or less works but it is difficult to manage, and often leads to hypoglycemia.

I used to ride by myself out in the boondocks far away from anyone while on MDI. You’ve no idea how scary that was for me. The worst day ever when riding my bike was when I had a flat tire on a deserted trail about 5 miles or more from my vehicle. My bg’s were dropping and I had a limited supply of carbs on hand. I’d say I was pretty freaked out all the way back. As soon as I got back to town I headed straight for the bike shop and asked how to prevent flats. That’s when I was introduced to Slime. Good stuff!

Years later I went on a pump and left so much anxiety over bg’s behind me. It doesn’t get much better than that. I’ve no problem doing any activity whatsoever be it climbing hills or riding bikes in the boonies. Fortunately I seldom do those things alone, but the reduction in anxiety is there thanks to first the pump, and secondly the Dexcom G5.

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I shoot for a low average blood glucose and a low standard deviation I tried to hit a standard deviation of less than 20 and really strive for teens if you can achieve both you will be 99% TIR

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Assuming you don’t have a lot of lows! You can have a low SD and low avg BG, yet not be in range if all your BGS are low!

Yes if you have a low aver BG and it is not in range, then you TIR will not be good.

I should have said if your BG is near your target and your Bg is in range and your standard deviation is low then your TIR will be very high,

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