title: Comparison of different enzyme-linked immunosorbent assay methods for avidity determination of antiphospholipid antibodies.
abstract: BACKGROUND
  Avidity of antiphospholipid antibodies may be clinically useful as a valuable additional characteristic. The aim of this study was to compare several ELISA modifications with different chaotropic agents and calculation of avidity indices for the determination of anticardiolipin antibody (aCL) avidity.
  
  
  METHODS
  We examined 28 serum samples with positive IgG aCL by adapted ELISA using various concentrations of urea and sodium chloride as chaotropic agents and different dilution of sera. We tested these conditions of ELISA-a single diluted serum sample with fixed concentration of a chaotrope and a serially diluted serum in the constant concentration of a chaotropic agent.
  
  
  RESULTS
  We demonstrated that ELISA method for avidity determination based on a single dilution of serum in the presence of fixed concentration of chaotrope is convenient for determination of IgG aCL antibody avidity. Concentrations 6 and 8 mol/L of urea or 1 and 2 mol/L of NaCl were suitable for sufficient dissociation of immune complexes during ELISA procedure.
  
  
  CONCLUSIONS
  This way was in good agreement with more demanding procedures. Both urea and sodium chloride may be used as chaotropic agents. Reference values of avidity indices essential for interpretation of patients' results must be established individually for distinct assay conditions.
authors.affiliation: Institute of Medical Biochemistry and Laboratory Diagnostics, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic.
authors.forename: Lenka
authors.initials: L
authors.lastname: Fialová
authors.affiliation: Institute of Medical Biochemistry and Laboratory Diagnostics, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic.
authors.forename: Milada
authors.initials: M
authors.lastname: Petráčková
authors.affiliation: Institute of Medical Biochemistry and Laboratory Diagnostics, First Faculty of Medicine, Charles University and General University Hospital in Prague, Prague, Czech Republic.
authors.forename: Oliver
authors.initials: O
authors.lastname: Kuchař
mesh_terms: D000328:Adult; D017153:Antibodies, Anticardiolipin / Q000097:blood* / Q000737:chemistry / Q000378:metabolism; D000915:Antibody Affinity; D004797:Enzyme-Linked Immunosorbent Assay / Q000379:methods*; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D012965:Sodium Chloride / Q000737:chemistry; D014508:Urea / Q000737:chemistry; D055815:Young Adult
chemical_list: D017153:Antibodies, Anticardiolipin; D012965:Sodium Chloride; D014508:Urea
keywords: 
  ELISA
  ; anticardiolipin antibodies; antiphospholipid antibodies; avidity; chaotropic reagents; serum; sodium chloride; urea