- advertisement -

math geeks, we need help

Discussion in 'Parents of Children with Type 1' started by frizzyrazzy, Jun 9, 2008.

  1. frizzyrazzy

    frizzyrazzy Approved members

    Joined:
    Dec 23, 2006
    Messages:
    14,141
    what on earth does this mean?

    http://care.diabetesjournals.org/cgi/content/short/dc08-0545v1?rss=1

    Translating the A1C Assay Into Estimated Average Glucose Values

    David M. Nathan, MD1, Judith Kuenen, MD2, Rikke Borg, MD3, Hui Zheng, PHD1,4, David Schoenfeld, PHD1,4, Robert J. Heine, MD2 and for the Alc-Derived Average Glucose (ADAG) Study Group From the1Diabetes Center, Massachusetts General Hospital and Harvard Medical School, Boston, MA
    the2Department of Endocrinology/Diabetes Center, VU University Medical Center, Amsterdam, the Netherlands
    3Steno Hospital, Copenhagen, Denmark; and
    the 4Department of Biostatistics, Massachusetts General Hospital, Boston, MA
    [SIZE=-1]dnathan@partners.org

    [/SIZE] [SIZE=+1]ABSTRACT[/SIZE]
    OBJECTIVE: The A1C assay, expressed as the percent of hemoglobin that is glycated, measures chronic glycemia and is widely used to judge the adequacy of diabetes treatment and adjust therapy. Day-to-day management is guided by self-monitoring of capillary glucose concentrations (milligrams per deciliter or millimoles per liter). We sought to define the mathematical relationship between A1C and average glucose (AG) levels and determine whether A1C could be expressed and reported as AG in the same units as used in self-monitoring.

    RESEARCH DESIGN AND METHODS: A total of 507 subjects, including 268 patients with type 1 diabetes, 159 with type 2 diabetes, and 80 nondiabetic subjects from 10 international centers, was included in the analyses. A1C levels obtained at the end of 3 months and measured in a central laboratory were compared with the AG levels during the previous 3 months. AG was calculated by combining weighted results from at least 2 days of continuous glucose monitoring performed four times, with seven-point daily self-monitoring of capillary (fingerstick) glucose performed at least 3 days per week.

    RESULTS: Approximately 2,700 glucose values were obtained by each subject during 3 months. Linear regression analysis between the A1C and AG values provided the tightest correlations (AGmg/dl = 28.7 [FONT=arial,helvetica]x[/FONT] A1C – 46.7, R2 = 0.84, P < 0.0001), allowing calculation of an estimated average glucose (eAG) for A1C values. The linear regression equations did not differ significantly across subgroups based on age, sex, diabetes type, race/ethnicity, or smoking status.

    CONCLUSIONS: A1C levels can be expressed as eAG for most patients with type 1 and type 2 diabetes.
     
  2. twodoor2

    twodoor2 Approved members

    Joined:
    Oct 30, 2007
    Messages:
    6,440
    Here's a good webpage that explains the R2 (best fit) and P-value of a linear regression model. Basically, all this means that after taking the values of AG and A1C levels for N sample size amount of individuals, they have found that the slope of the curve (a linear curve or in layman's terms, a line) that these points graph a close fit line that show a distinct correlation between AG and A1C levels. This is expressed in the equation given.

    AG = 28.7 x A1C – 46.7

    If you're familiar with X and Y, and linear equations, this could also be expressed as

    Y=28.7X - 46.7

    http://www.curvefit.com/linear_regression.htm

    This makes sense since Elizabeth's last A1C was 7.8, so if you do the math, her average AG was 28.7*7.8 - 46.7 or 177.16. Her meter average was 180, very close approximation.

    Linear regression models are used widely. Remember the ISF to I:C proportionality thread I started a while back? That was inspired by a linear regression model generated by sample sets of individuals taken by Dr. Allen King (a well known endo).
     
    Last edited: Jun 9, 2008
  3. frizzyrazzy

    frizzyrazzy Approved members

    Joined:
    Dec 23, 2006
    Messages:
    14,141
    YEs, this is what I needed. Is that formula good for everyone? I can see how it would be good to try it out because we always have our meter averages but we're always trying to guess what our a1c's are going to be.
     
  4. pfgordon1994

    pfgordon1994 Approved members

    Joined:
    Nov 3, 2006
    Messages:
    40
    Remeber that in the formula
    Y=28.7X - 46.7
    the Y is the average and the X is the a1c so if you want to figure out the a1c you would have to sub the average in for Y.
    For example if the average is 180 it would look like this:
    180 = 28.7X - 46.7
    You would add 46.7 to both sides and get

    226.7 = 28.7X and then divide by 28.7
    7.89... = X would be the a1c

    I hope this makes sense.
     
  5. frizzyrazzy

    frizzyrazzy Approved members

    Joined:
    Dec 23, 2006
    Messages:
    14,141
    thanks for showing how to do the reverse. Its been a long time since I had to figure this stuff out LOL

    but it would be interesting to see how it plays out the next time we all get A1c's.
     
  6. Brensdad

    Brensdad Approved members

    Joined:
    Dec 27, 2005
    Messages:
    2,383
    I like to watch race cars drive in big circles, and sometimes they crash.
     
  7. andeefig

    andeefig Approved members

    Joined:
    Mar 13, 2006
    Messages:
    1,616
    Say what?!??? :confused:

    Ok, maybe it's because I went to Art school, but WHAT THE HECK ARE YOU GUYS TALKING ABOUT????

    Is it OK that I have no clue? My mind just thinks differently.
     
  8. badshoe

    badshoe Approved members

    Joined:
    Jun 28, 2006
    Messages:
    2,153
    Ahhh... I only have 11 fingers and 10 toes I can't do the higher math...
     
  9. twodoor2

    twodoor2 Approved members

    Joined:
    Oct 30, 2007
    Messages:
    6,440
    According to the linear regression sample, the study states

    The linear regression equations did not differ significantly across subgroups based on age, sex, diabetes type, race/ethnicity, or smoking status

    Therefore I am under the assumption it is supposed to be good for everyone, but who knows for sure? Although they give a breakdown of the sample size on the diabetes type, they don't give a breakdown of the sample set based on the factors, age, sex, race/ethnicity, smoking status. In our case, I would be most concerned with the accuracy regarding age since that is probably the biggest factor here that we, as parents of type 1 diabetic children, are concerned with (I don't think any of our small kids smoke:p).
     
    Last edited: Jun 9, 2008
  10. mom2kenny

    mom2kenny Approved members

    Joined:
    Sep 30, 2006
    Messages:
    909
    LOL, They definitely have my mind going in those big circles!!!
     
  11. Jacob'sDad

    Jacob'sDad Approved members

    Joined:
    Nov 20, 2007
    Messages:
    3,803
    Didn't it say they used CGMS on the test subjects? I'm not going to read it again, I'm tired. If that is how they came up with their average BG then it has nothing to do with meter average. I can get a much better meter average for Jacob if I just stop checking him when I know he is high but will come down, like when we don't prebolus breakfast.
    If the formula works and the result actually matches the meter average then the person has done enough checking at the right times to even out the highs and lows. There are those that don't check between meals though, and their meter will not show all the highs that occurred during the day. If their a1c matches their meter average then they either have fantastic control or it's a miracle.
     
  12. twodoor2

    twodoor2 Approved members

    Joined:
    Oct 30, 2007
    Messages:
    6,440
    I think it was a combination of CGMS and blood glucose tests.

    AG was calculated by combining weighted results from at least 2 days of continuous glucose monitoring performed four times, with seven-point daily self-monitoring of capillary (fingerstick) glucose performed at least 3 days per week1
     
  13. Jacob'sDad

    Jacob'sDad Approved members

    Joined:
    Nov 20, 2007
    Messages:
    3,803
    I guess I should have read it again. I was thinking the finger pokes were to calibrate the CGMS. It looks like maybe it was more than that, however they still could have attempted to time the finger sticks to get a good balance of what was happening to BG throughout the day.
     
  14. twodoor2

    twodoor2 Approved members

    Joined:
    Oct 30, 2007
    Messages:
    6,440
    Like most studies, none are perfect and always have questionable values, or the sample is such that it calls into question how it is done. The p-value is low, so it is a good linear fit. It worked well for our meter average, but again, that's just one example.
     
  15. ADHDiabetic Mom

    ADHDiabetic Mom Approved members

    Joined:
    Apr 24, 2008
    Messages:
    644
    No clue. :confused: My math geek went to Camp Sweeney yesterday. :cool:
     
  16. moco89

    moco89 Approved members

    Joined:
    Mar 1, 2008
    Messages:
    2,430
    A1c => average BG

    1. A1c=7.5

    2. Subtract two from the A1c score
    7.5-2=5.5

    3. Then multiply by thirty
    5.5 X 30=165

    Therefore, your average blood sugar over the past three months was 165.

    This formula works because A1c is a linear function.
     
  17. twodoor2

    twodoor2 Approved members

    Joined:
    Oct 30, 2007
    Messages:
    6,440
    Hi Monica!!
    Your linear equation is slightly different than the one the study came up with. Your equation is

    AG=30A1C - 60

    or for fans of slope-intercept X,Y notation (see the OT thread on "Math Problems";))

    Y=30X - 60

    Stupid question, how did you come up with that?
     
    Last edited: Jun 9, 2008
  18. moco89

    moco89 Approved members

    Joined:
    Mar 1, 2008
    Messages:
    2,430
    One of my old doctors used that calculation. Also, some of the A1c charts you see in the doctor's offices match the formula I use, since A1c is a linear function.
     
  19. deafmack

    deafmack Approved members

    Joined:
    Sep 22, 2006
    Messages:
    3,209
    Learn ASL and then you only need one hand to count forever and two hands to do the higher math. hehe
     
  20. deafmack

    deafmack Approved members

    Joined:
    Sep 22, 2006
    Messages:
    3,209
    The formula seems to match an average blood glucose for whole blood. If I am right you have to add 15% to get the average blood glucose in plasma values. Here is a link to the chart for plasma values and then another link for the chart with whole blood glucose values.
    Plasma Values Link http://www.geocities.com/diabeteschart/bloodsugarchart.html
    Whole Blood Values
    http://www.geocities.com/diabeteschart/oldermeterus.html
    I tend to think in plasma values instead of whole blood because most meters are made to give plasma values.
     

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