Background:
The Department of Pathology and Laboratory Medicine is updating the collection and stability criteria for plasma ammonia in response to a recent field safety notice issued from the manufacturer.
Ammonia is an extremely unstable analyte and accurate measurement requires special attention during collection, transport, and processing. Ammonia should be collected in a lavender top tube (EDTA) and placed immediately on wet ice and transported to the laboratory for immediate processing. If immediate delivery of the specimen is not possible, the specimen must be centrifuged and aliquoted.
The aliquoted plasma should remain tightly capped on ice and delivered to the lab within 3 hours. Plasma collected with other anticoagulants (e.g. lithium heparin) will no longer be accepted.
Rates of spurious and artifactual ammonia increase are associated with erythrocyte and platelet count as well as with plasma activity of gamma-glutamyl transferase and alanine aminotransferase. If indicated, repeated ammonia sampling to exclude possible artifactual causes of high ammonia is recommended.
Effective date: April 20, 2022
Specimen requirement and testing information:
Specimen required:
1 mL of plasma collected in a lavender top (EDTA tube). Prior to blood collection: Prepare a container of wet ice deep enough to submerge tube up to blood level inside. Collect 3 mL of blood in lavender top (K2-EDTA) tube. Mix well and place immediately on wet ice. Deliver to the lab immediately. If immediately deliver is not possible the specimen must be centrifuged and aliquoted. Keep the plasma aliquot tightly capped and on wet ice and deliver to the lab within 3 hours.
Test methodology: Enzymatic Glutamate Dehydrogenase
Test code: AMMON
Minimum stability:
Ambient: Unacceptable
Refrigerated: 30 minutes on ice, or 3 hours after separation from cells and on ice.
Frozen: Unacceptable
Turnaround time (TAT):
STAT: 60 minutes
Routine: N/A
Set Up Days: Daily
Rejection criteria:
Specimens that exceed stated stability, unlabeled/mislabeled/mismatched specimens, and specimens submitted in leaking containers, or specimens received with insufficient amounts for testing. Clotted specimens. Specimens collected in heparin, oxalate, or citrate. Serum specimens.
References:
- Thermo Scientific Infinity Ammonia Liquid Stable Reagent Instructions for Use and Field Safety Notice. Available online at https://www.hpra.ie/docs/default-source/field-safety- notices/february-2022/v48119_fsn_1.pdf?sfvrsn=2
- Dukic L, Simundic A. Short-term and long-term storage stability of heparin plasma ammonia. J Clin Pathol 2015; 68:288-291.
A summary of all tests offered by our laboratory services can be found here: http://www.pathology.uci.edu/services/index.asp
Sincerely,
Bridgit O. Crews, PhD, DABCC
Director
Clinical Chemistry, Toxicology & Point-of-Care Testing
Edwin S. Monuki, MD, PhD
Chair
Department of Pathology & Laboratory Medicine
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