Antibodies to beta 2 glycoprotein I: standardized immunoassay and a reference interval for healthy controls

Patients with antiphospholipid syndrome (APS) demonstrate an antibody reactivity with beta 2 glycoprotein I (beta 2 GPI) independent of the anionic phospholipids that previously had been believed to be the relevant autoantigens associated with this syndrome. Immunoassays for IgG anti-beta 2 GPI have, however, suffered from a lack of standardization. In this article, we describe an assay based on reference standards that we developed recently. The assay exhibits excellent linearity, with regard to both application of the standards and dilution of out-of-range specimens. Precision was assessed both within the between run and was judged to be satisfactory. A reference interval was developed on the basis of a control group consisting of 111 men and 93 women, yielding a range of 0-19 standard IgG anti-beta 2 GPI units (SGU) for the ninety-fifth percentile of values. These data suggest that this standardized anti-beta 2 GPI assay may be useful in the clinical diagnostic laboratory.