Hi Nicola,
Ammonia is present in substantial amounts in platelets (enough to raise a
plasma ammonia from 20 to 120 umol/L (see attached letter from Clin Chem).
Thus you get higher results from heelprick and fingerprick samples and also
serum as the platelets have lysed in the wound or in the collection tube.
It is also necessary to prepare platelet poor plasma by spinning the sample
in a microfuge or equivalent as any remaining platlets in the sample will
lyse in the reaction vessel.
EDTA is hyperosmolar and in appropriate amounts may theoretically make the
platelets denser and easier to remove but also in theory in excess amounts
could make the platelets more fragile and easier to lyse. We did not do any
work on EDTA, we used Lithium Heparin tubes.
Best wishes
Dr David Cowley (Rtd.) Brisbane
-----Original Message-----
From: Clinical biochemistry discussion list
[mailto:[log in to unmask]] On Behalf Of Pullan Nicola (ROYAL
UNITED HOSPITALS BATH NHS FOUNDATION TRUST)
Sent: Thursday, April 28, 2016 11:01 PM
To: [log in to unmask]
Subject: Ammonia
Hello,
Can anyone help with the following?
1. Our pack insert (Cobas) states that EDTA blood tubes should be full
for ammonia analysis. We make no provision for this currently and don't
bounce requests if the bottles are under-filled. Any opinion?
2. If samples are separated from the cells and aliquoted into a sealed
false bottomed tube for analysis at a later point e.g. if analyser out of
action, any idea of stability?
Many thanks for any answers in advance.
Best wishes,
Nicola
Nicola Pullan
Principal Clinical Biochemist
Royal United Hospitals Bath NHS Foundation Trust Combe Park, Bath, BA1 3NG
Dir Line: 01225 824711 Visit our website at: www.ruh.nhs.uk/pathology
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