18 Responses

  1. Sysy
    Sysy December 20, 2010 at 6:32 am | | Reply

    Thank you for this post! It’s been on my mind lately…this standard deviation stuff. I asked my endo about it a few years ago and he said it is “irrelevant”. It makes sense to me that a lot of up and downs create havoc on the body. In fact, I think I live with some of the aftermath of swinging blood sugars. Now I try to keep my standard deviation really low. And my A1c. When will we catch a break? Thanks Amy :)

  2. Lloyd
    Lloyd December 20, 2010 at 6:59 am | | Reply

    I’m sorry, I just don’t buy into this 11% finding, not at all.

    We see it every day, people with high glucose are the ones having complications. The graphs from the UKPDS and DCCT show that what kind of diabetes you have does not matter for complications. High glucose does the damage.

    I shall continue to keep my glucose in the middle of the non-diabetic range (4.9 to 5.4) and SD at 14.


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  4. Lili
    Lili December 20, 2010 at 7:17 am | | Reply

    My endo definitely knows about standard deviation.

    I thought that standard deviation *was* known to factor into eye complications, though.

  5. Laura G.
    Laura G. December 20, 2010 at 7:30 am | | Reply

    Thanks for posting about SD! Intuitively I’ve known this for a long time–I feel my best when my SD is low. But I tried to ask my kind, thoughtful, old-school endo a question about my spiky management back in the early 90s and I still remember his answer: “Don’t worry, Laura. The body only sees the A1C.” But it makes sense to me that endos like mine and Sysy’s have labeled SD “irrelevant” up till now, because they’ve had no way to measure it!

    Seeing constant illustrations of my variability and grading it weekly or monthly has been the single best thing about having a CGM, and it’s what has helped me tweak my management and improve my daily health the most. What you can see, you can work on. Time for a big study on variability and complications using thousands of CGM patients’ data!

  6. val
    val December 20, 2010 at 8:16 am | | Reply

    Probably the reason standard deviation is inconclusive, is there there are different ways of measuring it. You have your post-low spikes (thud-boing!) and your overguestimated carbs (whoosh-splat) types of spikes, versus those nice little gentle waves I can rarely manage to achieve.

    So two people (or two days with the same person) may both have values that vary from 50 to 250, only in one of them you hit both within half an hour while with the other maybe they are low at 5am and high at 7pm and gradually drift in between.

    A real study of standard dev would need to fit all participants with CGM and calculate not only the stdev, and time spent out of ideal range, but also the rate of change on an hourly basis…Makes my head hurt, and I aced statistics in college :)

  7. Scott S
    Scott S December 20, 2010 at 8:19 am | | Reply

    In terms of quality-of-life, we as patients know that even if standard deviation has a relatively small influence on microvascular risk, it still spells major nuisance for people with diabetes, and the bigger question for people with type 1 diabetes (the standard deviation is, by definition, according to such endocrinologists as Dr. Zachary Bloomgarden, MD, almost always significantly higher in type 1 than it is with type 2) is how best to minimize it? There are many thoughts, for example, adding Symlin to the treatment protocol, but many patients find that can be more trouble than it’s worth and getting insurance coverage for it remains a challenge for some patients. The bottom line is that the doctor must work closely with the patient to decide how best to reduce standard deviation, and that may require more than the 15 minutes that the current U.S. payment system for healthcare reimbursement practically dictates. There is not a one-size-fits-all solution, but doing so may be worth the doctor’s investment!

  8. Erin
    Erin December 20, 2010 at 9:33 am | | Reply

    Point of clarification on what “low standard deviation” is–a given data set can have one no matter what the numbers are, as long as they don’t vary between too high and low a number. Someone who’s *always* at 200-225 would have a yucky A1C but still have a low standard deviation.

  9. Cary
    Cary December 20, 2010 at 11:56 am | | Reply

    As a kid growing up with diabetes it was fairly apparent that standard deviation never shows its face in A1C. It’s fairly common to have a “bad” standard deviation but an acceptable A1C and in some ways, fake a decent A1C.

    If you keep your A1C the same but reduce your standard deviation; you are actually improving your control. And there is no tool on the market that shows you that.

  10. Jim
    Jim December 20, 2010 at 5:49 pm | | Reply

    Well, at least your endo is looking at standard deviation. But what is “acceptable” for that statistic anyway? I think someone once told me that it was about 1/3 of the mean bg, but I don’t know where I heard it or whether that rule of thumb is accurate. Anybody have ideas on this??

  11. mcityrk
    mcityrk December 20, 2010 at 6:30 pm | | Reply

    Seems like you need a good idea of the overall daily trend of glucose data coming from an accurate CGM system to get an accurate calculation of standard deviation. Thus, most assumptions previously made about calculating standard deviation based on several discrete daily points from self-monitoring have so much inherent error in them that the concept of calculating percentage breakdown between A1C and standard deviation as causes of complications is questionable at best and possibly misleading at worst. The real question of course is if you have at this time a sufficiently large patient population satisfied in the quality of their CGM measurements that a summary meta study from this data is actually worthwhile.

  12. Penny
    Penny December 20, 2010 at 7:59 pm | | Reply

    I am a type 1 Diabetic and I am also what is called a Master Black Belt for Six Sigma, a fancy way of measuring processes and using statistics to prove systemic changes.

    The simple truth is that only 11% of the test results of the A1C correlated to complications. I have had a great A1C and I am a cyclist who exercises, yet I have had the worse year ever with all kinds of complications. I am underweight and not because of highs but because soo much has gone wrong, I have had a hard time with digestion. I do not have celiac nor any other contributing factors, except some pretty high variations with BS due to overeating and keeping sugars as tight as possible to achieve A1C of 6.0 I even had an A1C of 5.9 at one point.

    Most people say I look like the epitome of health and all I have to say is Thks, but if you only knew the year I had. I felt like I had been through chemo and nauseated all the time. it has taken me since May to keep food down. I finally have been able to eat almost normally in the last 3 weeks, although I still get hit every now and then. I am still losing some weight, but it has definitely slowed down. I have had 5 specialists looking into my situation and test after test. While they continue to look I am convinced I need to have better control and even if it means a higher A1C.

  13. Lloyd
    Lloyd December 20, 2010 at 11:42 pm | | Reply

    Well, at least your endo is looking at standard deviation. But what is “acceptable” for that statistic anyway? I think someone once told me that it was about 1/3 of the mean bg, but I don’t know where I heard it or whether that rule of thumb is accurate. Anybody have ideas on this??

    A type 2 on a pump can do better than 1/3 the mean bg, I do better than 1/6 the mean bg, though it took a few months to get that good at adjusting a pump.

  14. Lloyd
    Lloyd December 21, 2010 at 7:31 am | | Reply

    The simple truth is that only 11% of the test results of the A1C correlated to complications.

    Until this is confirmed by pier review, and confirmed my other studies, this is not so. That is the scientific method.


  15. susan f
    susan f December 21, 2010 at 8:42 am | | Reply

    Great article Amy, but certainly humbling and troubling to hear that microvascular complications are only roughly correlated with a1c’s!

    I too am one of those patients who did NOT have horrible a1c’s, except for a brief period pre-pump way back in college. I too suffered terribly with gastroparesis and slow digestion to the point of malnutrition and feeding tubes. One thing I can definitely say though is don’t give up. After a few years of better blood sugars, my digestion seems almost normal. To me, that is proof positive that good numbers improve nerve-system complications even if they are not as strongly correlated with microvascular complications.

    It seems I have autonomic neuropathy as manifested through digestive woes; I have however no kidney damage and no eye damage. It does seem that something else plays a role in damage.

  16. Ronnie the poor diabetic
    Ronnie the poor diabetic December 21, 2010 at 10:38 am | | Reply

    My endo said the score was irrelevant too…huh now you have me thinking I gotta look further into this….thanks amy

  17. Dennis
    Dennis December 29, 2011 at 3:48 pm | | Reply

    Well all I can say is after Getting D – Adult Onset at age 45 and it being in my Whole Family ( Mother & Siblings)?
    -I strove to get as low a BG’s as I could,striving for 80′s ave.
    -Had alot of hypo’s , ave 2–3 per day
    -had alot of Rebounds ( ave 200′s) too
    -But had 6% A1c’s !
    -Also got Retinopathy – 3 Eye Hemmorages over 2 yrs..
    - I thne stopped being so Aggressive and set the Bar Higher.. 100′s
    -I still Ave 6 -6.5% A1c’s and have alot less Lows and Highs and been 3 yrs and no new problems (yet)

    And yes, I think at least 50% of these ‘Complications” are out of our Control, We have a Auto Immune Disease the wants to Destroy every cell and organ in our body and we don’t have the Drugs to stop that process yet..

    Btwn Inaccurate Test meters, CGMS and Unstable Insulin Pumps and Not so Fast insulins, we lack the Right tools to do much better..

    Can have 100 BG’s 10x for the day and just 2 , 150-200 can throw the 12x ave, 24 hrs ave out of wack
    ave 120′s 8x and have 2, 175′s and your 130′s
    It’s so Frustrating getting a 170 after 2 hrs, after having such a “perfect day” going, isn’t it?

    Btwn Have to Know Exactly the Right Tot Carbs, Have to have 100 B4 eating and have to Kow the right Correction Bolus for 1,2 and 3 hrs to take if High..

    It just gets overwhelming and seeing as what’s the % of T1′s that are lucky enough to Get a Pump? 25%? what about the other 75%, they’re SOL, right?

    And oyu wonder why These Endo’s Are so Laid Back and don’t want us to Be so Aggressive?
    They know, Once you ave 7% or less A1c’s, the rest is upto That other 50-75% that we have no control over..

    And it’s In Medical Science and God’s hands..

    I still think, Getting Stem Cell Injections is the answer, even getting them once a Month is better than Nothing..
    If it cures our D? at least gives us Level 80-100 bg’s all the time? Count me in.. At least I won’t have to Inject myself 8-10x a day anymore and figur out all that complicated stuff and Fustrations..

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