Stephen
Thanks for raising this again.
I reluctantly changed from Li hep to B&D gel Vacationers some years
ago:
a. The lab analyser, an Orth. Vitros 950, had problems with measuring
plasma proteins.
b. It "simplified" lab processing.
c. We were seen as "difficult" by many medical staff, hospital and
general practice, as other local Pathology providers used serum. There
was management concern over loss of GPs as customers outweighed
provision of an accurate service.
We ask that urgent requests are sent in Li hep but very few are.
A survey of the labs in the South Thames regions at that time showed
only 2 using plasma.
The change was very effective for the lab processing. Single tube for
most tests, no more fibrin clots, no false "serum" lithium, cholesterol,
bands on electrophoresis etc. However I am concerned over the raised
potassium results we see - recalling an outpatient or GP patient to
check the plasma K+ is difficult.
Our computer now displays the F.C. data so that we can see increased
placeless etc.
How many hypokalaemias do we miss ??
Prof Joan Zilva, Westminster Hospital, published a paper on this more
than 20 years ago. Reference lost.
Average increase serum/vs plasma 0.3 mmol/L, range 0 - 1.1 mmol/L.
I collected 200 paired samples for normal ranges in the early 90s, all
carefully separated within 2 hrs, with very similar results. However
neither Zilva or I measured any F.C. parameters.
The evidence suggests that we should be using plasma.
Why do most of us persist in using serum ? Practical compromise ?
Is there enough evidence to support a national/international guideline
requiring the use of heparinised blood for potassium determinations ?
Paul
Dr Paul H Eldridge
Clinical Biochemist
University Hospital Lewisham
London SE13 6LH
UK
Phone: (44) 020 8333 3255
Fax: (44) 020 8690 8891
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