Anti-beta(2)-glycoprotein I ELISA: Methodology, determination of cut-off values in 434 healthy Caucasians and evaluation of monoclonal antibodies as possible international standards

Antibodies against beta (2)-glycoprotein I are among the most commonly dete cted subset of antiphospholipid antibodies. The inter-laboratory comparabil ity of results is hardly possible due to methodological differences, lack o f international standards and different cut-off values. We evaluated an ELI SA for the detection of anti-beta (2)-glycoprotein I using the analytical g oals based on biological variations for similar analytes (immunoglobulins). By our ELISA we fulfilled the optimal (IgA, IgM) or minimal (IgG) analytic al goals in longterm imprecision. The determination of cut-off values was b ased on the frequency distribution of results obtained on 434 healthy Cauca sians. To aim at a better inter-laboratory comparability we tested two mono clonal antibodies as possible calibrators: HCAL (IgG) and EY2C9 (IgM). Bind ing properties determined by dilutional curves showed great similarities wi th polyclonal sera, used as in-house standards. Cut-off values were express ed by concentrations of IgG and IgM monoclonal antibodies (4.5 and 25.3 mug /l). Our study shows the possibility for a successful application of analyt ical goals based on biological variation even when data for a particular an alyte are not available. The expression of cut-off values, obtained on a la rge scale Caucasian population, by the concentration of IgG and IgM monoclo nal antibodies could make possible a more reliable inter-laboratory compari son of data.