title: Elevated ammonia concentrations: potential for pre-analytical and analytical contributing factors.
abstract: BACKGROUND
  No study has explored the separate contributions of pre-analytical and analytical factors to hyperammonemia.
  
  
  METHODS
  Laboratory information systems were queried for tests of ammonia concentrations over a 12 month period. Pre-analytic (collection to laboratory receipt) and analytic (laboratory receipt to result) elapsed times were determined.
  
  
  RESULTS
  Under routine conditions for 3626 tests, normal and elevated results were similarly distributed if the time from venipuncture to result was <120 min. Delays, during analysis performance and in transportation to the laboratory, potentially contributed to hyperammonemia in a small number of samples (n=96, 2.7%). Similar results were obtained from a second hospital with a separate laboratory.
  
  
  CONCLUSIONS
  Delays, in either transportation to the laboratory after collection or before completion of analysis, have the potential to elevate ammonia concentrations and may cause pseudo-hyperammonemia. Unexpectedly elevated ammonia concentrations need to be evaluated for errors in sampling handling.
authors.affiliation: Department of Pathology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Parkland Memorial Hospital, Parkland Health and Hospital System, Dallas, TX 75235, USA. Electronic address: Ibrahim.Hashim@utsouthwestern.edu.
authors.forename: Ibrahim A
authors.initials: IA
authors.lastname: Hashim
authors.affiliation: Department of Internal Medicine, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA; Parkland Memorial Hospital, Parkland Health and Hospital System, Dallas, TX 75235, USA.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Cuthbert
mesh_terms: D000641:Ammonia / Q000097:blood*; D006801:Humans; D022124:Hyperammonemia / Q000097:blood / Q000175:diagnosis; D013048:Specimen Handling / Q000009:adverse effects*
chemical_list: D000641:Ammonia
keywords: Analysis delay; Post-analytic; Pre-analytic; Pseudohyperammonemia; Transportation delay