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RE: [IP] Glucose sensors - calibration and other technical details

Nanette Chana Freedman [mailto:email @ redacted] wrote:

> Setting aside my initial objections to a device 1) which does not give
> you immediate readout, thus enabling you to make useful adjustments,
> and 2) which only runs for 3 days, which for sure will not be 
> typical 3
> days (partly because for me no day is typical, and also 
> because as soon
> as I start doing something unusual like monitoring, I would quite
> likely become much more conscious of what I was eating, etc, making it
> still less typical), I decided that it would still be worth trying out
> in order to find out if there are unsuspected weird things 
> happening to
> my blood sugar, in addition to the weird things I already know about.

I think it's best to look at the CGMS as a big step in the right direction,
but still far from perfect, as much as anything for the reasons you say.  No
system for control enters as a complete package (Just ask Jan about how
pumps have changed over the past decade and longer!).  The system will
improve, and will most likely be a component in an effective closed loop
implanted system, AKA an artificial pancreas that will detect BG and adjust
insulin infusion accordingly.
> But now come my technical questions:  I understand that the device is
> calibrated to glucometer blood sugar readings, 4 readings daily.  That
> would be fine - I trust my glucometer readings, but what worries me is
> the accuracy of the calibration.  Apparently each day's readings have
> to be calibrated separately, because the performance of some component
> of the system is changing over the 3 days of its effective lifetime. 
> This gives me cause for concern about the accuracy of the 
> calibration -
> will it be as accurate at the end of each day as at the 
> beginning?  how
> well could such a calibration system work?  does anyone have any
> experience of this?  do all such devices currently available or under
> test rely on such systems? 

Once again, we're faced with the limitations of a waived status laboratory
test.  The CGMS meets those same standards as for our regular meters.  The
purpose of the CGMS is to spot diurnal cycles that impact control,
particularly at night.  It's also very useful for seeing how each of our
bodies processes the meals we eat, and can help us fine tune our bolus

When I used the CGMS several months ago (administered by MM as part of a
demonstration for Kaiser Permanente in Georgia -- I'm KP patient #1 for this
purpose), the nurse indicated that most people using the CGMS end up
increasing basal rates and reducing the insulin/carb ratio for bolus.  I
discovered a much more profound dawn phenomenon (and increased insulin needs
in the evening as well) and as a result increased my basals during those

Because the purpose is to spot these more general trends, and that the
accuracy/precision is the same as for our regular meters, there is no real
need for a capacity to immediately view the BG reading.  The one exception
to this would be for a reading outside of the target range to know whether
BG was going up or down, which might make a difference in how we adjust for

Jim Handsfield
mailto:email @ redacted OR
mailto:email @ redacted

The opinions expressed are my own and do not necessarily represent those of
my wife who runs this house and makes more important decisions than I do.
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