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Re: [IP] Serum glucose measurements

Celia McInnis wrote:
> The Precision QID meter claims to have "clinical accuracy" -
> which, I think, means that they try to make a guess at the
> blood serum glucose measurement from the whole blood sample.

Actually it doesn't, their claim is that the meter is accurate despite
use of certain drugs or other situations that make other meters have
inaccurate results. For instance smome vitamins are known to affect
bg levels with certain meters, theirs supposedly corrects for this (or
avoids the problem).

> Earlier (Dec 9 1998), Michael Maturen had said that the
> difference between serum and whole blood glucose
> measurements is about +12% and he said that various meters
> essentially upped their whole blood glucose reading by 12%
> to report readings in line with serum bg levels.

True, though the 12% varies by manufacturer. Some use 8%, some use 12.
It depends on their view of what the difference is.
> Questions:
> 1. Does anybody have any explanations for why I consistently
> measure higher than the labs with both of my Precision QID
> meters? (If it was one meter/lab, I'd suspect the meter/lab,
> but since it's 2 meters/labs, I'm less likely to suspect the
> meter/lab) - For example., what is the 12% conversion
> adjustment for whole to serum readings (which Michael
> Maturen referenced) based on?

Serum blood glucose is done by taking blood from a deeper
vessel than our bg meters use, which makes it different already.
THEN they centrifuge the blood to remove some of the water, 
resulting in concentrating the glucose. SO they are measuring 
a different thing and changing it further by mecahnical means.

Incidentally, if they took blood with a syringe and gave you
a sample from that, it will NOT be accurately measured by 
your meter, which is calibrated for fingertip capillary blood. 
You really need to do a fingerstick at the same time tehy take 
veinous blood to have any accuracy at all.

> 2. Is there a reason why the conversion adjustment might
> work less well for me at some times than at others? (I had,
> for instance, just cycled 20 km before arriving at the lab,
> if that has any relevance, and I had had two other low
> readings already that day (with my meter reading as low as
> 2.0 (I can only hope that THAT reading was not a 70%
> overstatement...))).

I don't think the conversion makes a difference, it's most 
likely caused by what I said above, and/or a difference in 
the test itseslf. Meters can vary somewhat from slight
differences in sample size, room temperature or timing.

> 3. Do we get some glucose benefit from something other than
> the serum? - for example from the hemoglobin?

It isn't really a benefit, the blood is just a carrier for 
the glucose. NOt sure, but I think the hemoglobin is what the
glucose attaches to, the serum is just the chemical/cell mix
in the blood, minus the water.

Ted Quick
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