Dear Colleagues,
We receive ammonia samples from external laboratories and rural/remote areas, which may not have been handled optimally. Recollection of theses samples can be very challenging and results in significant delays. We assay these samples in communication with the clinical/metabolic team. My personal view is; as most interference's cause an increase in plasma ammonia results, a normal result from a non-optimal sample may potentially exclude a hyperammonaemia. I also think a POC ammonia meter could prove useful in these remote areas for IEM patients needing frequent ammonia monitoring.
I would also like to raise awareness of rapid sample processing and analysis required for acute lymphoblatic leukaemia patients receiving Asparaginase therapy. Asparaginase catalyses the reaction of asparagine to aspartate generating ammonia. Laterza et al found a mean increase in plasma ammonia results of 24%, after a mean re-analysis time of 12mins, in patients receiving Asparaginase therapy. The laboratory I work in has also experienced this.
Kind regards
Corey Markus
Medical Scientist.
Automated Laboratory, SA Pathology.
Women's and Children's Hospital Site.
Adelaide, South Australia
Ph: 08 81616704 or 0414756577
Email: [log in to unmask]
________________________________________
From: Clinical biochemistry discussion list <[log in to unmask]> on behalf of Jonathan Kay <[log in to unmask]>
Sent: Friday, 29 April 2016 7:54 PM
To: [log in to unmask]
Subject: Re: Ammonia
It’s like the mid-1980s all over again! When we did the audit of availability of metabolic investigations close to where babies were born and managed the major deficit was plasma ammonium.
The only thing I’d add to David and Mick’s comments is that if you are studying this you can’t do it with ammonium alone. The children with IEM and similar will also have high plasma glutamine etc and the transport and handling may cause degradation. IIRC that’s what turned us against ever freezing the specimens.
Jonathan
> On 29 Apr 2016, at 09:13, Henderson Mick (LEEDS TEACHING HOSPITALS NHS TRUST) <[log in to unmask]> wrote:
>
> Dear Colleagues,
> can I urge extreme caution when enforcing policies that result in the rejection of samples for ammonia analysis.
> At the very least such a policy must be discussed with the clinical users of the service.
> Hyerammonaemia, at levels above 350umol/L, is likely to be a medical emergency with potentially irreversible consequences for brain function and may be lethal.
> There is a balance to be struck between the obligation to report accurate results with the clinical imperative to identify dangerously aberrant biochemistry.
> Clinical teams are much more likely to quickly repeat a blood test when presented with a high result on a 'delayed' sample.3
> Such results must, of course be accompanied by an appropriate warning and must be telephoned.
> We are aware of clinical catastrophes caused by the rejection of samples that were then not repeated for 24 hours, for a variety of reasons.
> If a patient has an inborn error of metabolism the metabolic crisis can deepen rapidly.
>
> Best Wishes,
>
> Mick Henderson
>
> From: David Cowley <[log in to unmask]>
> Subject: Re: Ammonia
> Date: 29 April 2016 at 05:23:36 BST
> To: <[log in to unmask]>
> Reply-To: David Cowley <[log in to unmask]>
>
> 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.
>
> ________________________________________
> From: Clinical biochemistry discussion list [[log in to unmask]] On Behalf Of Gavin Murdock [[log in to unmask]]
> Sent: 28 April 2016 22:13
> To: [log in to unmask]
> Subject: Re: Ammonia
>
> 1. Ammonia in plasma exists in equilibrium with the ammonium anion. Ammonia is also present in the atmosphere. When the sample is collected there is the possibility of the equilibrium being disturbed by the addition or loss of ammonia to the air space.
>
> To mitigate against this affect we only analyse samples that arrive in the lab within 15 minutes of collection. You could reject grossly under-filled specimens but my experience is that such specimens are likely to be haemolysed and so would be rejected on that basis - ammonia is present in red cells at ~3 times the concentration of plasma.
>
> 2. The key step is to separate the plasma from the cells. Once that has happened ammonia still increases due to deamination reactions but at a slower rate. Low temperatures retard these reactions and so increase the stability.
>
> We allow promptly separated plasma to be refrigerated if it can be analysed within 2 hours, otherwise it should be frozen.
>
> Gavin
>
> On 28 April 2016 at 14:00, Pullan Nicola (ROYAL UNITED HOSPITALS BATH NHS FOUNDATION TRUST) <[log in to unmask]<mailto:[log in to unmask]>> wrote:
> 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<http://www.ruh.nhs.uk/pathology>
>
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