Richard,
I posted something similar before Christmas, please find the summary of responses below. Thanks to Angela for the WHO paper (number 5 below).
I could not find accepted "standards" to audit against. Many labs have their own policy but timings etc are variable. One could argue scientifically that samples should be separated within 2 hours. However pragmatism is required to balance clinical and scientific requirements. Locally I have set up a standard to audit against. The standard is that "95% of samples should be centrifuged within 4 hours of collection".
I can confirm that if a laboratory is not in charge of, or does not have budget for, its own transport then this a challenging standard for samples coming from community phlebotomy. I am now going through the process of attempting to change the transport design, as well as placing centrifuges in key locations in the community.
Regards
Martin Myers
Question: As part of a transport review I am auditing the time taken from phlebotomy to separation of serum from cells by centrifugation.
There is local discussion about which standard should be used for the audit. Folklore would suggest that unseparated samples start to become unsuitable at 4 to 6 hours (ignoring temperature and glucose for the moment) and the laboratory makes a "judgement call" on samples received later than this time. However Tietz states that "Plasma or serum should be separated from cells as soon as possible, and certainly within 2 h", referenced to Laessig et al, Am J Clin Pathol, 1976:66;598-604. I would be grateful if anyone had references or evidence about which standard we should be working to.
Answers:
1. If you are using BD Vacutainer gel tubes, BD state: 'Gel separation tubes should be centrifuged no later than 2 hours after collection'. See: http://www.bd.com/vacutainer/faqs/#tubes. I wonder how many labs can achieve this in practice (not us!)
2. Is that a trick question ? I haven't seen one, but if you look in helpful text books like Tietz they say things like "...recommendation for the most reliable K+ determinations is to collect blood with heparin, to maintain it between 25-37 degC, and to separate within minutes by high-speed centrifugation.." Hence we fail !
3. I have a paper that addresses some of the issues on the effect of delayed centrifugation. A scanner copy in pdf form was sent to the mailbase on Wednesday. It may not have been reached all members on the list as it is too large a size for normal e-trafficking. The article ref is: Delay in centrifugation and measurement of serum constituents in normal subjects.
M. S. Devgun, in Clinical Physiology and Biochemistry, 1989; 7: 189-197. A copy of the pdf file is available on the jismail archive that can accessed via the ACB web site. Alternatively, please contact Manjit Devgun directly for a copy.
4. It sounds as if your determining standards for preanalytical variables. I'm not sure you'll find what you need here, but one useful source might be the book: See review: http://www.ifcc.org/ejifcc/vol13no1/1301200107.pdf
5. See p10 of WHO guidelines 2002 (attached)
<<who preanalytical guidelines2002.pdf>>
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Richard Stott
Sent: 11 January 2007 12:49
To: [log in to unmask]
Subject: GP Specimen transport timing.[Scanned]
Hi everyone
I realise this is something of an old chestnut and the adverse effects
of delay have been discussed to death. Despite that there does not seem
to be any consensus or robust evidence as to what is an acceptable time
from vein to centrifuge.
We are making some progress with one of our PCTs and are looking for
benchmark data to support their case for funding two pickups per day
from practices. The improvement aims to achieve a maximum 4 hours
between phlebotomy and arrival of the sample at the laboratory.
What do other laboratories actually achieve?
Thanks
Richard Stott
Principal Clinical Scientist,
Biochemistry,
Doncaster & Bassetlaw hospitals NHS Foundation Trust.
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