Since the potassium-concentration of the plasma in an EDTA-tube is raised appr.7 times, and the sodium-concentration in a citrate-tube only 1.5 times, the EDTA-tube is definitely the most "dangerous" to precede a tube for electrolyte measurements.
Med venlig hilsen,
Martin Kjærulf Nielsen
chefkemiker
Klinisk biokemisk afdeling,
Centralsygehuset i Næstved
DK4700 Naestved, Danmark.
Tlf. +45 5572 9000....4043
>>> "Simpson Elliott (MK) Top Grade Biochemist, Laboratory Directorate" <[log in to unmask]> 18-02-03 10:11:27 >>>
We've certainly had problems with high potassium levels, accompanied by low
calcium, magnesium & Alk Phos levels if they're done, due to the EDTA
specimen being taken before the U&E, so I would expect citrate to do the
same.
Elliott
-----Original Message-----
From: Trevor Gray [mailto:[log in to unmask]]
Sent: 17 February 2003 22:28
To: [log in to unmask]
Subject: Order of draw
Dear colleagues,
We have been reviewing our instructions to phlebotomists in regard to
the order of draw for venous blood samples. Becton-Dickinson, supplier
of our tubes recommends following the NCCLS guidelines which suggest the
following order:
"The following order-of-draw, which is recommended when drawing
several specimens during a single venepuncture, is based on pragmatism.
Its purpose is to avoid possible test result error due to cross
contamination from tube additives. This procedure should be followed for
both evacuated tubes, and syringe transfer of blood to multiple tubes.
(1) Blood culture tube
(2) Plain tube, non-additive (e. g., red stopper)
(3) Coagulation tube (e.g., blue stopper, citrate)
(4) Additive tubes:
? Gel separator tube
? Heparin (e.g., green stopper)
? EDTA (e.g.., lavender stopper)
? Oxalate/fluoride (e.g.,gray stopper)"
This seems to be counter-intuitive in that the chemistry tube (gel
separator) is drawn after the sodium citrate tube. The rationale seems
to be to avoid contaminating the citrate tube with clot activator, but I
would have thought that contamination from citrate into the clotted tube
more likely.
Has anyone any experience, anecdotal or otherwise (from a statistically
respectable sample !) which proves the case one way or the other ?
Trevor
--
Trevor Gray
Dept. of Clinical Chemistry,
Northern General Hospital,
Sheffield S5 7AU
0114 271 4309
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