Comparison of different enzyme-linked immunosorbent assay methods for avidity determination of antiphospholipid antibodies

BackgroundAvidity 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. MethodsWe 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 ELISAa single diluted serum sample with fixed concentration of a chaotrope and a serially diluted serum in the constant concentration of a chaotropic agent. ResultsWe 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 8mol/L of urea or 1 and 2mol/L of NaCl were suitable for sufficient dissociation of immune complexes during ELISA procedure. ConclusionThis 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.