title: Preanalytical factors of importance for measurement of Chromogranin A.
abstract: BACKGROUND
  Studies indicate that fasting and diurnal variation can influence serum Chromogranin A (CgA) concentrations and furthermore, stability of the CgA molecule has been questioned. We investigated the impact of pre-analytical conditions on a CgA assay.
  
  
  METHODS
  Serum CgA concentrations were measured in blood samples collected from ten healthy subjects at three time points during three days with and without fasting. Samples were kept at 4°C and re-measured after 24 and 48 h in order to test the stability of the measured epitopes. For establishment of a reference interval, serum samples were collected from 120 healthy individuals.
  
  
  RESULTS
  Serum CgA concentrations did not vary between fasting and non-fasting individuals (p=0.74), nor between gender (p=0.66). The analytical imprecision was 4.3%, the within-subject variability was 11.9%, while the between-subject variability was as high as 50.2%. Serum CgA concentrations measured during the day did however not differ (p=0.30). Of importance, re-analysis at 4°C showed significant decay in the CgA concentrations after 24 h (mean decrease 15.6%) and 48 h (mean decrease 44%). The median CgA concentration in 120 healthy subjects was 41.2 ng/mL with a reference interval of 30.3-94.4 ng/mL (2.5-97.5 percentile).
  
  
  CONCLUSIONS
  Fasting does not influence CgA concentrations significantly, while sample stability is a major issue with the assay tested. The biological variation of CgA was defined and a reference interval was established.
authors.affiliation: Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense C, Denmark. Electronic address: lise-pedersen@rsyd.dk.
authors.forename: Lise
authors.initials: L
authors.lastname: Pedersen
authors.affiliation: Department of Clinical Biochemistry and Pharmacology, Odense University Hospital, Sdr. Boulevard 29, 5000 Odense C, Denmark.
authors.forename: Mads
authors.initials: M
authors.lastname: Nybo
mesh_terms: D000328:Adult; D000368:Aged; D016477:Artifacts; D001774:Blood Chemical Analysis / Q000379:methods*; D053379:Chromogranin A / Q000097:blood*; D005215:Fasting; D005260:Female; D006801:Humans; D007118:Immunoassay; D008297:Male; D008875:Middle Aged; D055815:Young Adult
chemical_list: D053379:Chromogranin A
keywords: Biological variation; Chromogranin A; Neuroendocrine tumor; Pre-analytical phase; Quality requirements; Reference range