title: Short-term and long-term storage stability of heparin plasma ammonia.
abstract: OBJECTIVE
  Ammonia is an extremely unstable analyte and requires special attention during sampling, transport and storage. The aim of this study was to evaluate the stability of ammonia in lithium-heparin plasma during short-term (at +4°C) and long-term (at -20°C) storage.
  
  
  METHODS
  Twenty plasma samples were used for short-term stability assessment. Each sample was divided into five aliquots and stored in stoppered tubes at +4°C, for 1, 2, 3, 4 and 24 h from initial testing. Fifteen plasma samples were used for long-term stability assessment. Each sample was divided into eight aliquots and stored in stoppered tubes at -20°C for 3, 24, 48 h and 1, 2, 4, 8 and 12 weeks from initial testing. Ammonia concentration was determined on a Beckman Coulter AU2700 chemistry analyser using Randox ammonia enzymatic UV method. Bias was calculated from initial value for each time point and compared with quality specifications defined by Royal College of Pathologists of Australasia.
  
  
  RESULTS
  The average bias exceeded the total allowable error after storage of samples for 1 h at +4°C and 3 h at -20°C.
  
  
  CONCLUSIONS
  Ammonia is not stable during storage at +4°C and -20°C in lithium-heparinised plasma and should therefore be analysed immediately.
authors.affiliation: University Department of Chemistry, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Lora
authors.identifier: http://orcid.org/0000-0001-6690-7551
authors.initials: L
authors.lastname: Dukic
authors.affiliation: University Department of Chemistry, Medical School University Hospital Sestre milosrdnice, Zagreb, Croatia.
authors.forename: Ana-Maria
authors.identifier: http://orcid.org/0000-0002-2391-5241
authors.initials: AM
authors.lastname: Simundic
mesh_terms: D000641:Ammonia / Q000097:blood*; D000925:Anticoagulants / Q000494:pharmacology*; D015982:Bias; D015415:Biomarkers / Q000097:blood; D020099:Coated Materials, Biocompatible; D003080:Cold Temperature; D015925:Cryopreservation; D004867:Equipment Design; D006493:Heparin / Q000494:pharmacology*; D006801:Humans; D018020:Lithium Compounds / Q000494:pharmacology*; D018962:Phlebotomy / Q000295:instrumentation*; D015203:Reproducibility of Results; D013056:Spectrophotometry, Ultraviolet; D013997:Time Factors
chemical_list: D000925:Anticoagulants; D015415:Biomarkers; D020099:Coated Materials, Biocompatible; D018020:Lithium Compounds; D000641:Ammonia; D006493:Heparin
keywords: METHODOLOGY; QUALITY ASSURANCE; STORAGE