title: Measurement of nitric oxide-related amino acids in serum and plasma: effects of blood clotting and type of anticoagulant.
abstract: BACKGROUND
  Analysis of circulatory amino acids is performed in diverse fields of research, but very often without justification or even specification of specimen type. We investigated the impact of coagulation and anticoagulants on amino acid concentrations, with emphasis on amino acids involved in nitric oxide metabolism.
  
  
  METHODS
  Plasma, using either heparin or EDTA as anticoagulant, and serum were collected from 23 apparently healthy subjects. Amino acids were measured with high precision using high-performance liquid chromatographic techniques.
  
  
  RESULTS
  Compared to heparin-plasma, the concentrations of almost all amino acids were lower in EDTA-plasma and higher in serum. For EDTA-plasma the mean difference was highest for tryptophan (5.3%). The mean difference between serum and heparin-plasma was much higher for some amino acids, including taurine (42.3%), arginine (36.4%), glutamic acid (16.2%) and serine (5.6%).
  
  
  CONCLUSIONS
  Differences in amino acid concentrations between EDTA- and heparin-plasma are small and clinically most likely irrelevant. Concentrations of amino acids in serum are higher than in heparin-plasma, which is probably caused by poorly controllable ex vivo release from blood cells during clotting. We advocate using plasma rather than serum and not using different anticoagulants interchangeably in a single study. In addition, we urge editors and reviewers to demand adequate description of specimen type in manuscripts.
authors.affiliation: Metabolic Laboratory, Department of Clinical Chemistry, VU University Medical Center, Amsterdam, The Netherlands.
authors.forename: Mariska
authors.initials: M
authors.lastname: Davids
authors.forename: Job H C
authors.initials: JH
authors.lastname: Peters
authors.forename: Sigrid
authors.initials: S
authors.lastname: de Jong
authors.forename: Tom
authors.initials: T
authors.lastname: Teerlink
mesh_terms: D000596:Amino Acids / Q000032:analysis*; D000925:Anticoagulants / Q000737:chemistry*; D001777:Blood Coagulation; D004492:Edetic Acid / Q000737:chemistry*; D006493:Heparin / Q000737:chemistry*; D006801:Humans; D009569:Nitric Oxide / Q000378:metabolism; D010949:Plasma / Q000737:chemistry*; D044967:Serum / Q000737:chemistry*
chemical_list: D000596:Amino Acids; D000925:Anticoagulants; D009569:Nitric Oxide; D006493:Heparin; D004492:Edetic Acid