A Dose of Dr. E: Standard Deviation

“Standard Deviation” can sound like an intimidating term, but all it means is how much our blood sugars bounce around from day to day. It can be a really useful tool to help us know what times of day we’re in range, and where we might need to pay a little bit more attention and make some adjustments.


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    Thanks Steve for your simple, straightforward SD explanation. I have been pushing this with members of our monthly Type 1 group. Most of them give me a “deer in the headlights” gaze, thinking it’s too.complex to understand. When I show them my Dex plots; Mean 148 (SD 48), they are all envious.. Your video helps explaining it better.
    There may be hope yet. Ha! All the best, Jack

    • Jack…thanks so much for your kind comments. It is hard to understand for many who do not live and breathe this stuff every day. Hope you are well.

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    I have always thought since having CGM data that SD should be more emphasized along with A1C, but it has been difficult to find what it considered a good number. I get frustrated with myself seeing T1D’s below 6.5 A1C (that is amazing! 6.7 was my best) and feel I should be doing better, but after watching your comments I guess I’m doing not so bad 43-50 SD (striving for below 40 but that does not seem to last), A1C avg.7. Life has so many variables each day, it’s tough. Thanks so much for all your online information!

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    thank you for your information on SD. I have been Type 1 for 18 years and never really knew how that worked. My Endocrine doc doesn’t even look at that, just my A1C [which at last count was 9], and says lets check again in 3 months and see if we can get that down. I am trying to be very pro-active in my treatment and gather as much information as possible. How were you and your patient that you showed in the video able to manage her SD? I am a bouncer and very frustrated.
    Love all your videos and trying to get to California next week for the TCOYD conference. Thank you for all you do to help the Type 1’s out there.

    • Hi Janae,
      The key for my patient was to make sure her basal dose was correct, and we adjusted that based on her fasting overnight, looking at her CGM and then adjusting her dose. Hope that helps!

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    Hi, Steve
    Loved hearing your great info at the TCOYD Type 1 conference in San Diego this year.
    I’m a DYI Looper and was told Basel rates should be about the same all day as well as the Carb to Ratio, but per your video (which makes a lot of since) my stardand deviation really needs to be changed.
    My friend Gayle ( head of Diabetic Sisters in Ventura) talked to Rayhan Lal at the conference and he said also that our loop system setting should be about the same all day.
    Do you think the setting should be the same or more variable thru the day.

    • Hi Melva,
      I am not looping yet, but Jeremy Pettus can answer your question face to face if you’re able to come to our conference in San Diego on November 17th.

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    What is a normal(non diabetic) persons SD? Have had the big D for 58 years, and just can’t stop a 32 SD. I have worked very hard for a 5.7 A1C, but the SD is 32. I am always searching for new info. My Pediatrician patted me on the back, and told me not to cry..I would live to a good 36, at 9 that was old so I stopped crying. I am 30 years passed that, but think of the prehistoric ways to manage back then. So lucky to still be here, and relatively healthy. I do normally run a low before I eat to stop the big spike. I know, but I do not work and can stay on top of the little low. I do understand that is probably how my SD is so high, but if I didn’t it would be the same with a spike of high. : (
    Thanks so much for any help

    • Hi Linda, a non diabetic person’s SD is 20 mg/dL. SD in people without diabetes does not vary much. Anything less than 50 for someone with diabetes is considered excellent! Sounds like you have really figured out your own strategy to keep your A1c down. A standard deviation of 32 is incredibly good. You should be very proud – it’s better than mine!

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    Hi dr Edelman,
    Hi from Ireland! My daughter is T1, aged 16 months when she was diagnosed and has been on the dexcom and tandem Tslim now for almost 3 months.

    Thank you so much for your clear explanation on your video, it’s the first time I have understood SD. Our endocrine team are lovely but only look at A1C (which has gone from 83mmol at diagnosis to 53mmol now)

    So a long winded question! The insulin suspend function will often be triggered but we still avoid hypos and manage to have a low SD at the moment for the past 2 day readings, she is at 1.9mmol/32.4. If her SD is good and she is in range 80%+ of time and avoiding hypos, how much of an issue is the pump suspend?

    Thanks so much in advance

    • Wow…your daughter is doing well. Avoiding hypos with a TIR of 80% is pretty darn good. I wear the Tandem Control-IQ and you basically should trust it to turn off at the right time for the right length of time. Stay well!

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    Thanks for this. My doctor told me my a1C was 5.3 and then followed it by saying “Your standard deviation is great, too.” Made a mental note to Google that later. I saw on my CGM app that my average glucose is 104 and my SD is 34. Had no idea what that meant. Thanks for explaining.

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