title: A WHO reference reagent for the Serum Transferrin Receptor (sTfR): international collaborative study to evaluate a recombinant soluble transferrin receptor preparation.
abstract: BACKGROUND
  The usefulness of serum transferrin receptor (sTfR) as a marker of iron deficiency is limited by lack of standardization of commercial immunoassays for sTfR. An international collaborative study was performed to evaluate a lyophilized preparation of recombinant soluble transferrin receptor (rsTfR) for its suitability to serve as a World Health Organization (WHO) Reference Reagent to standardize immunoassays for sTfR.
  
  
  METHODS
  The concentration of pure rsTfR was determined from the A(280 nm) using the adjusted theoretical extinction coefficient and molecular weight calculated from its sequence, before dilution and lyophilization in a sTfR-depleted serum matrix. Six manufacturers and a health protection laboratory assayed the candidate Reference Reagent, coded 07/202, along with three lyophilized serum samples, using commercial assays for sTfR.
  
  
  RESULTS
  Dose-response plots demonstrated acceptable overall parallelism between 07/202, manufacturers' in-house standards, and serum samples. However, there was poor agreement on the estimated (r)sTfR content of 07/202 and serum samples. Expressing the sTfR content of the serum samples relative to 07/202 markedly improved agreement between methods.
  
  
  CONCLUSIONS
  Use of 07/202 would reduce inter-method variability. The preparation was established as the 1st WHO Reference Reagent for sTfR with assigned free rsTfR monomer values of 21.7 mg/L and 303 nmol/L (0.5 mL reconstitution).
authors.affiliation: National Institute for Biological Standards and Control, Potters Bar, Hertfordshire, UK. susan.thorpe@nibsc.hpa.org.uk
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Thorpe
authors.forename: Alan
authors.initials: A
authors.lastname: Heath
authors.forename: Giles
authors.initials: G
authors.lastname: Sharp
authors.forename: James
authors.initials: J
authors.lastname: Cook
authors.forename: Richard
authors.initials: R
authors.lastname: Ellis
authors.forename: Mark
authors.initials: M
authors.lastname: Worwood
mesh_terms: D007118:Immunoassay / Q000379:methods / Q000592:standards*; D007202:Indicators and Reagents; D055550:Protein Stability; D011990:Receptors, Transferrin / Q000097:blood* / Q000235:genetics; D011994:Recombinant Proteins / Q000097:blood / Q000235:genetics / Q000592:standards*; D012015:Reference Standards; D015203:Reproducibility of Results; D014944:World Health Organization
chemical_list: D007202:Indicators and Reagents; D011990:Receptors, Transferrin; D011994:Recombinant Proteins