title: Increasing hCG concentrations during storage at (+)4 degrees C with the Bayer Centaur Total hCG method.
abstract: BACKGROUND
  The interpretation of changes in serum human chorionic gonadotropin (hCG) concentrations in early pregnancy requires a knowledge of the day-to-day imprecision of the method at the concentrations measured. We therefore attempted to determine the analytical imprecision of our total hCG method over a 4-week period at concentrations up to 20,000 IU/L.
  
  
  METHODS
  Serum specimens with hCG concentrations between 100 and 20,000 IU/L were collected during early pregnancy and analysed using the Bayer Centaur Total hCG method at weekly intervals after storage at (+)4 degrees C and (-)20 degrees C.
  
  
  RESULTS
  The reproducibility of hCG results over a 4-week period in refrigerated specimens with an initial hCG concentration below 1000 IU/L was poor (mean coefficient of variation = 17.4%) and there was an apparent increase in serum hCG concentrations of up to 68%. Similar changes occurred in some specimens stored at (-)20 degrees C. Further experiments confirmed that significant increases can occur during the first week following specimen collection.
  
  
  CONCLUSIONS
  Total hCG concentrations in serum specimens collected during early pregnancy increase significantly during storage when measured by the Bayer Centaur Total hCG method, possibly due to a conformational change in hyperglycosylated hCG. When this method is used for monitoring early pregnancy, specimens should ideally be analysed on the day of collection.
authors.affiliation: Department of Clinical Chemistry, Royal Hallamshire Hospital, Sheffield, S10 2JF, UK. kevin.page@sth.nhs.uk
authors.forename: K
authors.initials: K
authors.lastname: Page
authors.forename: J
authors.initials: J
authors.lastname: Gomez
authors.forename: N
authors.initials: N
authors.lastname: Smith
mesh_terms: D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D003080:Cold Temperature; D005260:Female; D006801:Humans; D011247:Pregnancy; D011259:Pregnancy Tests, Immunologic; D011933:Reagent Kits, Diagnostic; D012680:Sensitivity and Specificity; D013997:Time Factors
chemical_list: D018997:Chorionic Gonadotropin, beta Subunit, Human; D011933:Reagent Kits, Diagnostic