Theory may not always match reality and I do not think you can
assume that whole blood levels will always equal plasma results when
using electrodes for measurements.
We have several ABL 725 analyzers and perform monthly
comparisons on a few samples to confirm agreement. (whole blood versus
plasma from those whole blood samples). The glucose results from the
ABL match the plasma glucose levels reliably, in our experience. (I
don't have data handy, but can forward comparison data at a later date).
The close match of the results is likely a result of electrode design
and the calibrators.
On the other hand, glucose meters are (or were) notorious for
generating different results on whole blood and plasma and only recent
changes to the design of the test strips reduced the impact of
hematocrit on some meter models. There are a number of reports
published on the impact of hematocrit on electrolyte measurements by
ISE. It may be that glucose enzymatic-biosensors are less prone to
hematocrit effects that potentiometric electrodes, but I'm certain that
generalization can be made. Those are my thoughts...... Regards, Andrew
Dr. Andrew W. Lyon
Univ. Calgary, Calgary, AB, Canada
-----Original Message-----
From: clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of John Whitfield
Sent: May 7, 2002 7:05 PM
To: [log in to unmask]
Subject: Glucose measurements in blood gas analysers - whole blood or
plasma?
I have been asked whether glucose results from our blood gas analyser
are equivalent to plasma glucose or whole blood glucose. This arose from
a discussion of whether we should quote a different reference range
depending on the method of analysis.
My preliminary scientific answer is that the electrode is in contact
with the plasma phase of the whole blood and therefore the result given
is the plasma glucose (just as the potassium result is the plasma
potassium).
On the less scientific and more practical side, one could say that since
no-one is going to run their GTTs through this kind of system, and
anyone who gets a blood gas sample analysed is pretty sick, a few
percent difference doesn't really matter anyway.
The system in question is the Radiometer ABL 725, but the principle
should apply to any electrode-based system. Does anyone have a contrary
opinion, or data, so we don't have to do a comparison?
thanks
John Whitfield
Clinical Biochemistry
Royal Prince Alfred Hospital
Sydney, Australia
Phone (+61) 2 9515 5246
Fax (+61) 2 9515 7931
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