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There have been a few reports of falsely low ammonia results using lithium heparin as a preservative. We tried using Li Hep tubes with the Roche method and saw this effect with a couple of samples. The results were very low/'negative'.
http://www.clinchem.org/content/38/9/1921.full.pdf
http://www.ncbi.nlm.nih.gov/pubmed/16678809
Tanya
Dr Tanya Hart
Clinical Biochemist
Department of Clinical Biochemistry
Poole and Royal Bournemouth Hospitals
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of COLLINS MICHAEL (RM1) Norfolk and Norwich University Hospital
Sent: 22 June 2012 10:04
To: [log in to unmask]
Subject: Re: ammonia assay Roche platforms
The problem with ammonia on a U&E sample is that you need to ensure the sample is not too old.
We were, at one time, rejecting 50% of our ammonia samples because they were too old on receipt.
We now insist on a special sample for ammonia. What's special about this sample is that it is a normal Li heparin tube with a distinctive coloured label chosen by a poll of labs staff as the most obvious colour. They have to pick up the tube from the lab so we note the time the tube is collected and the requesters must note the time of collection. The label states that the tube must be in the lab no later than 20 minutes after the blood is collected. I know that ammonia is more stable than this but it ensures quick delivery of the sample.
Ammonia samples have a unique suffix to prevent accidental sampling of the test from a routine sample received at the same time.
Since this system started we have not rejected any ammonia samples.
Mike Collins
BMS3
Biochemistry Automation
Norfolk & Norwich University Hospital
England
-----Original Message-----
From: Clinical biochemistry discussion list [mailto:[log in to unmask]] On Behalf Of Cowley, David
Sent: 21 June 2012 19:29
Subject: Re: ammonia assay Roche platforms
Hi Paul,
We have run ammonias successfully for many years on LiH samples on a Vitros platform. You have to spin the sample hard enough to make platelet poor plasma (there is a lot of ammonia in platelets). You can check you are acheiving this by doing plasma platelet counts on the haematology analyser. The routine spin for U and E is usually not hard enough to get rid of the platelets.
Kind regards
Dr David Cowley
Director of Chemical Pathology
Mater Health Services Brisbane
________________________________________
From: Clinical biochemistry discussion list [[log in to unmask]] On Behalf Of Paul Thomas [[log in to unmask]]
Sent: Wednesday, 20 June 2012 10:17 PM
Subject: ammonia assay Roche platforms
Roche recommend K-EDTA plasma for ammonia assays, does anybody have any experience or evaluation data on lithium heparin plasma? It would be much easier to run it on the U&E sample.
Thank you for your help
Paul
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