- advertisement -

What exactly does the A1C measure

Discussion in 'Parents of Children with Type 1' started by nanhsot, Nov 29, 2011.

  1. nanhsot

    nanhsot Approved members

    Joined:
    Feb 20, 2010
    Messages:
    2,626
    Not looking for the standard "average blood sugar over 3 months" type answer here, I mean what EXACTLY does it measure and how? I understand it measures the amount of sugar attached to the hemoglobin. I get that a red blood cell (hemoglobin) lives about 3 months, so that's where the 3 months factors in, but exactly how does high blood sugar equate to high A1c?

    Is it more a factor of high blood sugars that are sustained/not dealt with and therefore the sugars crystalize on the hemoglobin? How exactly does a high A1C reflect an AVERAGE blood sugar? I mean, if you have a really bad week, will that reflect in it? What if you are high all the time but it's because you are eating all the time, so the blood sugar never has a chance to stablize but there IS enough insulin in the system to match the food??

    I'm not making any sense! My son has had a HORRIBLE 3 months of numbers. Football + eating non stop + late nights + early mornings + eating no stop......

    His A1C is fine. While I am thankful that his health hasn't suffered there's a bit of confusion and now he's left with the feeling that tight control isn't that big a deal. It's like if your kid quit practicing their music but then made first chair in the symphony...you're happy and proud, but realize that not practicing was just rewarded! I was actually kind of hoping for a bit of a wake up call, but instead he left the appointment rather smug!

    How is it possible to see a meter and Dexcom average well into the 200s and see an A1C under 7?

    The kid eats non stop, and it's maddening actually. Trying to test bolus or basal is near to impossible. He never goes more than 2 hours without eating another meal. (he's also athletic and muscular, so not fair).

    My own theory is that he matches food to insulin very well (he does actually do so) so the while the blood sugar is high a lot, it's matched by insulin so it isn't around long enough to crystalize/attach to the hemoglobin.

    Any other thoughts?
     
  2. selketine

    selketine Approved members

    Joined:
    Jan 4, 2006
    Messages:
    6,055
    We have the opposite issue lately with the meter averages being very typical of what it has always been but his a1c went up substantially. He is on a cgms (off of it for a few weeks in the past 3 months because we switched systems) and I find that his Dexcom tends to want to read higher (sometimes a good bit higher) than what his fingerstick is.

    It makes me wonder if his meter is reading him too low or something.

    The a1c was done by the same lab we've always used.

    I can't figure out if it is possible to get a wonky a1c number back from the lab or what. I don't think we are missing any sustained highs. His a1c corresponds more to his DEX average but when he is high his Dex will say something like 226 and I test and he is 168 (for example).

    In your case the only thing that could explain it is unknown lows but I don't think you'd have such persistent lows if he is using a Dex regularly. Our meter average is in the 100's and his a1c is 8.5 - highest I've ever seen it!
     
  3. SueM

    SueM Banned

    Joined:
    Mar 25, 2010
    Messages:
    380
    While I don't have any studies to back this up... I have a feeling (again, not stating this as "fact"), that the last few weeks are much more heavily weighted than the previous weeks/months. Has he cracked down over the past few weeks a bit knowing that he had an appointment coming up? ;). When I have had more tight control in the weeks before an appointment we have often times seen a significantly better A1C than in those times when the most recent numbers have been higher.

    Also, is he a consistent pre-boluser? Our endo puts TONS of weight on better A1C's for those who pre-bolus consistently. Obviously, the idea behind it makes sense. We have been trying hard to improve on that. Been a bit more challenging with my daughter being old enough now to grab her own snacks.

    Whatever he's doing... It's impressive to have an A1C lower than 7... We haven't seen that in years (if ever, to be honest). I can understand how it may be frustrating though when you are trying to get him to be more consistent, etc.
     
  4. nanhsot

    nanhsot Approved members

    Joined:
    Feb 20, 2010
    Messages:
    2,626
    Gosh no, we went yesterday, the Monday after Thanksgiving (and my family had a second Tgiving dinner on SUNDAY!). His week before was horrendous.

    He does prebolus though, well, maybe half the time.

    Yes, it is impressive and I'm very happy, just...puzzled. His numbers look horrible lately, though they are improving now that football is over and his schedule is a bit more reliable.
     
  5. Christopher

    Christopher Approved members

    Joined:
    Nov 20, 2007
    Messages:
    6,771
    I will let the "experts" answer but one thought may be that even though he goes high, if you bring that number down relatively quickly there is less impact to the overall A1C. Did you ask the Endo their opinion on this topic?
     
  6. swellman

    swellman Approved members

    Joined:
    Jul 30, 2008
    Messages:
    3,543
    Wikipedia

    EDIT: I have no experience to comment on the "4 weeks to 3 months" vs "2 to 4 weeks". It wold be very helpful if anyone had data what shed light on this subject. I would expect someone who had, for instance one 3 month period with good control and associated A1c and another 6-8 week of good control followed by a 2-4 week of poor control and it's associated A1c. If their A1c value were very similar then I would lean towards the 3 month side and if they saw a significant difference then I would lean towards the 2 week side.
     
    Last edited: Nov 29, 2011
  7. Brenda

    Brenda Junior Member

    Joined:
    Oct 19, 2005
    Messages:
    683
    Found this on the web site:

    Question:
    From Lincoln, Nebraska, USA:

    I understand that the A1c correlates to the average blood sugar over the last three months (with more recent readings having a greater impact), but what type of hyperglycemia raises the A1c result the most? Is it transient high readings of greater than 250 mg/dl [13.9 mmol/L] that are corrected quickly or more frequent levels of less than 250 mg/dl [13.9 mmol/L] that persist for several hours?

    I ask because my most recent A1c was lower than I had expected at 5.2%. I usually have a fasting sugar below 100 mg/dl [5.6 mmol/L]. My highs can be upwards of 300 mg/dl [16.7 mmol/L], but I correct them quickly and I am rarely high for more than a few hours.

    Answer:

    That question can be tested mathematically, but I don't have the immediate answer. In theory, the amount of glucose elevation over time determines the value. If you have just a short amount of time with elevated blood sugars, that would be preferred to smaller incremental changes over a longer time. Realize there are several situations that may provide similar results.



    Several years ago, someone explained to me that the glucose attaches to the red blood cells once the BG hits 150 mg/dl. Of course, a 150 on a home meter can be off + or - by 20% so this may contribute to the discrepancy. A 300 mg/dl BG 80 days ago will not affect the A1c as much as a 300 mg/dl BG last Monday (assuming the A1c is done this week). Furthermore, I think that a 300 last Monday will have a greater affect than a 200 last Monday. I am not sure that it is possible to be precise because RBCs are dying all the time and BGs are changing all the time, if that makes any sense.
     
  8. TheFormerLantusFiend

    TheFormerLantusFiend Approved members

    Joined:
    Sep 10, 2006
    Messages:
    4,925
    Glucose attaches to hemoglobin at all blood sugar levels- nondiabetics do not have A1cs of 0%- I've never heard of one below 2% and normal is roughly 4-6%.

    More recent blood sugar affect A1c more because of the lifespan of the hemoglobin cells; more of your red blood cells that you have right now were alive 2 weeks ago vs 2 months ago. The lifespan of a red blood cell (which is basically a bag of hemoglobin) is roughly 4 months. The more sugar in the blood, and the older the blood cell, the more sugar it has crashed into.

    The A1c is actually a pretty bad predictor of any individual's average blood sugar because of the differences between people in red blood cell life span. There may also be an issue with the test done for the A1c- particularly if the A1c was done with a meter in the doctor's office, the meter may simply be very inaccurate. Ellen recently posted a link to a study of A1c meters that found that most of the A1c meters are really inaccurate.
     
  9. MommaKat

    MommaKat Approved members

    Joined:
    Sep 2, 2011
    Messages:
    646
    I'm posting more in response to the context of why you asked, and your concerns about the take away your son gets from this. Glycosylation is really just a fancy term for the addition of carbohydrate to a specific amino acid in a protein that makes the protein functional. (Proteins are chains of amino acids that twist and fold, but that's another story ;) ) Usually this is caused by the presence of an enzyme, but in this case as the red blood cell is exposed to glucose over the course of it's life time, a dextrose molecule from glucose attaches to an end amino acid of the hemoglobin forming hemoglobin A1C (glycosylated hemoglobin). You know how some sugars and syrups are stickier than others, well, think of this as the stickiest. Once they attach it's basically irreversible, making it a good thing to measure. Whether this attachment occurs depends on two things, blood glucose concentration (the higher it is, the more likely) AND the duration of high concentration, which is why HA1C is really a measure of glucose levels over time, and it's really an average of how much attachment occurs over time, so you could have great control for six weeks, not so good for two, and still walk out with a great looking A1C. (and vice versa...)

    There are some things that can affect A1C that don't really relate to blood glucose control but change the measure you get. Sometimes the life of red blood cells is shortened, like in anemia, times of prolonged and intense exercise (football and weight lifting come to mind...) Because the life of the RBCs is shorter this will result in a decreased HbA1C, but that's because duration of exposure was decreased, not because of better glucose control.

    You mentioned that you think it's possible that he just matches his food with insulin really well, which may be the case, and would decrease the duration of the high, and therefore the amount of glycosylated hemoglobin. The thing to keep in mind there is that HbA1C is just a tool. Any time bg is elevated the extra glucose molecules cause microvascular damage, so his A1C could look great, but if he has a lot of spikes, that tool just isn't reading and giving the two of you an average indicative of the times he's had high bg and resulting microvascular trauma, which is additive over time.

    Not sure if I just made that more confusing, but I hope not. It does tell you why we need both HbA1c and pre / post bg numbers for the best possible control. One's a 4x6 and the other a panoramic, but neither gives us the whole picture. I like to think of pre /post tests as the means of getting enough of the small pictures that we can create a flip book closer to a movie which takes place on the backdrop of the panoramic.
     
  10. swellman

    swellman Approved members

    Joined:
    Jul 30, 2008
    Messages:
    3,543
    Has this been quantified in any way? I'm not questioning the accuracy but, since we have pretty good A1c levels I would like to "take it to the next level". Any reference(s) would be appreciated.
     
  11. wilf

    wilf Approved members

    Joined:
    Aug 27, 2007
    Messages:
    9,652
    No, it hasn't. But it is the current thinking among a subset of the Type 1 medical community.
     
  12. SarahKelly

    SarahKelly Approved members

    Joined:
    Nov 14, 2009
    Messages:
    1,147
    This idea was actually brought up to us at dx with Isaac, since we already had a background in t1d and management/tools we asked deeper questions right off the back. When questioning about the A1C, BG fluctuations and how to lessen the effects of t1d on the rest of his body she stated that it was better to reduce the BG fluctuations than over worry about his A1C. She stated that she'd rather see a smoother BG around 140 than for him to be bumping between 30 and 250 all day as that would cause more damage. She keeps to the idea of a lower A1C, but still at every appointment really focuses upon his standard deviation and how we are trying to tighten control in order to keep the small blood vessels from being damaged and causing further damage.
    At the time of dx she did have papers on this topic, I will see if I can locate them as they have been shoved aside in the "diagnosis hospital binder" which I wasn't fond of having around.
    I do know that she continues to do research at UW therefor some of her ideas for treatment may still be more theory based and less research at this time. That said I trust her choices.
     
  13. MommaKat

    MommaKat Approved members

    Joined:
    Sep 2, 2011
    Messages:
    646
    Quantified? Not that I can find. The studies seem to be focusing more on how is the microtrauma caused, and investigation into different theories re the mechanism of action. For instance, one theory is that high levels of insulin lead to plaque formation - but that does not seem to be demonstrated in recent research (and if it did, relates more to poor control and / or insulin resistance leading to more consistent use of higher levels of insulin. I do have one of those studies bookmarked, but no longer have access :( )

    Studies with qualitative / theoretical support, yes. I have to look up titles since I no longer have access to the journal database, but this is behind the argument for tight control, and the basis of my difficulties with dd's current endo. Her feeling is that too tight control results in hypoglycemic unawareness and is therefore dangerous in children. (Okay, given our issue with lows, I can see that), but in the long term scheme if tight control reduces her risk of CHD, retinopathy etc., then doesn't tight control make more sense in a 'whole life' approach? (I'm not suggesting I know the answer to that, btw, it's what I'm struggling with, and why I've started correcting higher bg values despite our being told not to yet.)
     
  14. swellman

    swellman Approved members

    Joined:
    Jul 30, 2008
    Messages:
    3,543
    No offense intended but that's not terribly helpful without a context ... what subset? A majority? Minority? Researchers or clinicians?

    I would like to see that if you ever run across it.

    That would be great.

    It's unfortunate that we, the average internet googler, don't have access to a number of journal articles.
     
  15. wilf

    wilf Approved members

    Joined:
    Aug 27, 2007
    Messages:
    9,652
    I'd say a significant minority of researchers. But it's all speculative at this point. Here's an article that explains the thinking.

    If you want more just google "blood glucose, variability" and read up to your heart's content.. :cwds:
     
  16. Cookie Monster

    Cookie Monster Approved members

    Joined:
    Jan 5, 2009
    Messages:
    131
    Do you have a link, Wilf. Not sure if you meant to put in a link or not but I'd really like to read up on this. Fascinating thread.

    I find MommaKat's dilemma over limiting the highs and any resultant long-term damage at the risk of lows strikes home with us. I believe I have a duty to my son to be as informed as possible, even if the answers aren't yet definitive.
     
  17. wilf

    wilf Approved members

    Joined:
    Aug 27, 2007
    Messages:
    9,652
    Sorry, here it is:
    http://www.mendosa.com/minimal_variability.pdf
     
  18. swellman

    swellman Approved members

    Joined:
    Jul 30, 2008
    Messages:
    3,543
  19. swellman

    swellman Approved members

    Joined:
    Jul 30, 2008
    Messages:
    3,543
    It seems to me that standard deviation is the next logical step in control/complications.
     
  20. SarahKelly

    SarahKelly Approved members

    Joined:
    Nov 14, 2009
    Messages:
    1,147
    our son's endo figures his standard deviation from the CGM data along with his BG readings. Is this not how it should be figured?
    I honestly love that his endo is focused on this aspect rather than the A1C, that said she also is very honest about how she is having TJ and I treat Isaac's diabetes "aggressively" since she knows we check frequently and aren't scared of trying new ideas to gain tighter control. From her statement I drew the conclusion that it would be a bit more tough for people not frequently checking or utilizing a CGM.
    Wilf, thanks for that pdf :)
     

Share This Page

- advertisement -

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice