I'd be glad of comments from users of the Roche (Hitachi, previously
Boehringer) 917 on the following phenomenon, & particularly from USA and
UK/Europe to see if it is worldwide.
About the beginning of December, we noticed that our internal QC values for
chloride would drop when a new electrode was installed and then they would
climb by about 6 mmol/l at higher values (e.g. 118 to 124 or more) over the
next two to three days. Unfortunately this first occurred at the time we
were switching to a new supply of unassayed QC material so we don't know
which value is "right". However we don't believe it is due to faulty QC
material, because we have now shown that it occurs with material from two
different sources and with patient samples as well.
Enquiries have revealed that other local users of 917s have seen this
problem too. Interestingly, two local labs using the Roche Integra (which
may or may not use similar electrodes?) had this problem when they were
using gel tubes but not since switching to non-gel tubes. So our current
view is that this phenomenon is an interaction between the current batch of
917 chloride electrodes (it didn't seem to happen until about five or six
weeks ago, although the electrodes have never been all that wonderful) and
the use of gel tubes (presumably the gel coats the electrodes gradually and
changes the response to the calibrator, and to patient or QC samples, in
some differential way). It doesn't affect the sodium or potassium
electrodes.
So my specific questions are:
- has this happened elsewhere?
- does it happen with other systems?
- do you think that gel is likely to be part of the explanation?
- what (apart from dropping the use of gel tubes, which we would be
reluctant to do) can be done about it?
Any other comments welcome.
John Whitfield
Clinical Biochemistry
Royal Prince Alfred Hospital
Sydney, Australia
Phone (+61) 2 9515 5246
Fax (+61) 2 9515 7931
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