Antiphospholipid IgG Certified Reference Material ERM^®-DA477/IFCC: a tool for aPL harmonization?

Area of Science:

• Immunology
• Clinical Chemistry
• Reference Materials

Background:

• Antiphospholipid syndrome (APS) diagnosis relies on detecting specific autoantibodies.
• Harmonization of laboratory methods for anti-beta2-glycoprotein I (anti-β2GPI) IgG is crucial for accurate APS diagnosis.
• Existing diagnostic methods show variability, impacting patient care.

Purpose of the Study:

• To evaluate the Certified Reference Material (CRM) ERM^®-DA477/IFCC for its ability to represent anti-β2GPI antibody heterogeneity in APS patients.
• To assess the CRM's efficacy in calibrating IgG anti-β2GPI laboratory methods.
• To determine if the CRM can improve the harmonization of anti-β2GPI IgG assays.

Main Methods:

• Characterization of CRM reactivity against different domains of β2GPI using specific assays (QUANTA Flash^®, in-house ELISAs).
• Evaluation of CRM's anti-Cardiolipin (anti-CL) activity using various immunoassay platforms (QUANTA Lite^® ELISA, QUANTA Flash^® CLIA, EliA™ FEIA).
• Assessment of CRM's calibration performance across four anti-β2GPI IgG methods using clinical samples and controls.

Main Results:

• CRM demonstrated high anti-domain-1 and no anti-domain-4-5 activity, reflecting APS patient antibody profiles.
• Acceptable dilution linearity was observed for anti-CL assays (R² 0.957–0.997).
• Calibration with CRM improved comparability between anti-β2GPI IgG assays, achieving 85% concordance compared to 66% with assay-specific calibration.

Conclusions:

• The CRM ERM^®-DA477/IFCC effectively represents the heterogeneity of anti-β2GPI/CL antibodies found in APS patients.
• The CRM has the potential to significantly improve the harmonization of anti-β2GPI IgG assays.
• Achievable harmonization levels are influenced by the inherent selectivity differences among various diagnostic assays.