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Diabetic controlling blood sugar, Spreadsheet to estimate HbA1c
Re: Diabetic controlling blood sugar, Spreadsheet to estimate HbA1c -- Posted by Jim Dumas on 09-27-03 09:28
R. loanguy wrote:
> Hello everyone:
>
> I am relative newcomer to these groups, but I would like to share
> something that I came up with to estimate my HbA1c levels. I have been
> following the advice about the monitoring after meals in order to keep
> good control of blood sugars, but could not find out anywhere in the net a
> place that would let me estimate the impact that said control would have
> on my HbA1c levels.
>
> As most of you are aware, a diabetic must try to keep this percentage
> under 6.5% in order to get better odds at not developing complications.
> Because I could not find a tool to do this, I came up with one of my own
> by working a formula to estimate the average blood sugar using HbA1c.
>
> I created a small one page site for people to go download it. I would
> appreciate it if people with data and an actual HbA1c test result would
> try it out and tell me how accurate it is.
>
> The spreadsheet can be found here:
>
> http://www.loanuniverse.com/Diabetes/
Hi R,
HbA1c prediction was discussed in great detail about 2 months ago on MHD.
So I don't want to rehash the details again.
Basically, besides the sampling issue Charly mentioned, (i.e., Nyquist
sampling requirement for the AUC [integral] of the glucose profiles), your
model does not account for the red blood cell lifespan. 90 days of BG
averaging only accounts for 90 day old RBCs. But what about the new RBCs
made today? They have no glycosylation yet but are in the blood sample
drawn for the lab test of HbA1c. In short, the plasma compartment acts a
mixing vat for daily RBC cohorts and the mathematics must account for these
newer RBCs somehow. Also note that people without spleens will have longer
RBC lifespans and your model will have to find these values as well. (FYI,
the textbooks say RBCs live an average of 120 days in normals.)
Next, there are seasonal variations in HbA1c where 2 Swedish MDs (Diabetes
Care 12/96 if memory serves me) measured ~0.5% (converted to Bio-Rad HPLC
equivalent by me as it was about 0.8% for their methodology) yearly
variation in HbA1c in about 800-1000 patients over 10 years. Max was in
January and minimum was in July. I suspect the pineal gland in the brain
controls this hormonally and your model must account for this variation.
So your model is too simplistic to work universally for all DMs,
--
Jim Dumas
T1 4/86, background retinopathy, rarely hypoglycemic: <1/mo.
lispro+R+U+NPH daily, moderate exercise, typically <6% HbA1c
Re: Diabetic controlling blood sugar, Spreadsheet to estimate HbA1c -- Posted by Jim Dumas on 09-27-03 13:54
R. loanguy wrote:
> I await your feedback.
Hi R,
I decided to look for the seasonal variation of HbA1c DC reference. It is:
Seasonal variation of HbA1c in adult diabetic patients, Johan Asplund,
Diabetes Care, v20 #2, Feb 1997, p. 234.
500 to 800 patients beginning in 1987 for 8 years of data. 55% are type 1s.
HbA1c is measured via ion-exchange chromatography with reference < 5.2% as
normal. So this is a different method than used in the DCCT with the
Bio-Rad HPLC instruments: ref < 6.05% normal. Total HbA1c samples of
11,473. Average January HbA1c peak of 7.61% and July nadir of 7.23%
(student's t test P < 0.0001!). So we have a difference of ~0.4% (round to
tenths) that must be converted to the US DCCT equivalent somehow. So I
guessed 0.5% for the US DCCT equivalent. The paper concludes patients have
better control in the summer and thus the lower HbA1c values.
But I disagree. I've kept BG data for myself since May, 1986. I don't make
any changes to my computer controlled insulin dosing and thus my BG control
is identical in January versus July. Exercise is likewise identical and
diet has little difference (more fresh veggies maybe). But I see an
average 0.7% summer-winter constant mean BG difference in HbA1c with the
Bio-Rad HPLC measured HbA1c over 1992 to 1999. I started using a computer
to dose in 1990 after a serious hypoglycemic event while driving my car.
This forced me to take action with tools available and I've not had another
ER visit since.
I also have taken great pains to use one BG meter assay methodology to keep
the BG data comparable over the years. This was all with the AccuChek III
double assay (two color Chemstrip bG) meter that is highly respected for
its accuracy. I have also forced my endos to use a lab that has the "Gold
Standard" Bio-Rad Diamat HPLC or equivalent HbA1c assay methodology to keep
the HbA1c assays comparable.
So my personal data hypothesis is the seasonal variation is caused by an
hormonal influence much like the artic fox's immune system slows down in
the winter months to conserve resources. This observation can be refined
easily now that OTC A1cNow kits are available. These assays are biased to
be equivalent to the DCCT methodology at a 7% HbA1c. They read slightly
higher when below 7% and slightly lower when above 7% per the professional
product literature in the Metrika 10 pack kits.
Thus my model (and yours by implication) must account for this variation.
The seasonal variation is real. What causes it is debatable,
--
Jim Dumas
T1 4/86, background retinopathy, rarely hypoglycemic: <1/mo.
lispro+R+U+NPH daily, moderate exercise, typically <6% HbA1c
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