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[IP] Serum glucose measurements

On Wednesday I had my serum bg level measured at a lab. I
always compare with my meter - a Medisense Precision QID -
and so I had the technician take some blood from the test
tube and place it on the strip in my meter (via a pipette).
I got a reading of 3.4 mmol/l (62 mg/dl), which felt
accurate to me. I was  hungry but was certainly in full
control of my faculties. I had no trouble cycling the 2 more
km to get home for supper.

Well, an hour or two later I got  a phonecall from the lab
saying that they measured me at 2.0 mmol/l (36 mg/dl) (they
rechecked their results) and wanted to make sure that I was

So - my reading was 70% higher than theirs! So far, I have
always measured higher than the labs  with my meter (and I
have tried 2 different labs and 2 different Precision
meters),  but I have always been within 15% until this

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.
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.


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?

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%

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


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