title: Investigations of blood ammonia analysis: Test matrices, storage, and stability.
abstract: An assessment of blood ammonia concentration is common medical practice in the evaluation of an individual with an unexplained mental status change or coma. The determination of a blood ammonia level is most commonly done using a glutamate dehydrogenase (GLDH)-based assay, although there are many potential sources of artifact and the literature is inconsistent regarding key preanalytic issues. Using a GLDH-based assay, we first investigated matrix effects using three anticoagulants: heparin, EDTA and oxalate. Heparin-anticoagulated plasma was substantially less precise than EDTA- and oxalate-anticoagulated plasma. Oxalate-anticoagulated plasma showed a greater baseline of apparent ammonia than either heparin- or EDTA-derived plasma, presumably due to interferants. We then evaluated the stability of EDTA-anticoagulated plasma for assessment of ammonia when stored at 4°C,-14°C or -70°C. There was a linear increase of ammonia with storage at both 4°C and -14°C. Plasma kept at -70°C for up to three weeks showed no change in measured ammonia relative to the baseline determination. This work clarifies preanalytic conditions for which a precise determination of ammonia can be accomplished using a GLDH-based assay.
authors.affiliation: Cleveland Clinic Lerner College of Medicine, United States.
authors.forename: Brittany N
authors.initials: BN
authors.lastname: Goldstein
authors.affiliation: Pathology and Laboratory Medicine Institute, United States.
authors.forename: Jordan
authors.initials: J
authors.lastname: Wesler
authors.affiliation: Cleveland Clinic Lerner College of Medicine, United States; Quantitative Health Sciences, Cleveland Clinic, United States.
authors.forename: Amy S
authors.initials: AS
authors.lastname: Nowacki
authors.affiliation: Pathology and Laboratory Medicine Institute, United States.
authors.forename: Edmunds
authors.initials: E
authors.lastname: Reineks
authors.affiliation: Cleveland Clinic Lerner College of Medicine, United States; Pathology and Laboratory Medicine Institute, United States. Electronic address: natowim@ccf.org.
authors.forename: Marvin R
authors.initials: MR
authors.lastname: Natowicz
mesh_terms: D000328:Adult; D000641:Ammonia / Q000097:blood*; D000925:Anticoagulants / Q000737:chemistry; D001793:Blood Preservation; D015925:Cryopreservation; D004492:Edetic Acid / Q000737:chemistry; D006493:Heparin / Q000737:chemistry; D006801:Humans; D008297:Male; D010070:Oxalates / Q000737:chemistry; D013997:Time Factors
chemical_list: D000925:Anticoagulants; D010070:Oxalates; D000641:Ammonia; D006493:Heparin; D004492:Edetic Acid
keywords: Ammonia; Hyperammonemia; Plasma