Comparison Between Chemiluminescent Assay and Enzyme-Linked ImmunoSorbent Assay Techniques for the Detection of Anti-Cardiolipin and Anti-β2 Glycoprotein I Antibody Values

Background: Antiphospholipid antibodies (aPLs) are essential for antiphospholipid syndrome (APS) diagnosis, which is based on clinical and laboratory parameters, including the detection of lupus-anticoagulant (LAC), anti-cardiolipin (aCL) and anti-β2-glycoprotein-I (aβ2-GPI) antibodies. The enzyme-linked immunosorbent assay (ELISA) is the reference methodology for classification criteria, although chemiluminescence immunoassays (CLIA) are more common in clinical practice. Methods: Since LAC reflects the functional activity of a large subset of antiphospholipids, through coagulation assays that enhance a phospholipid-dependent inhibitory effect, it has been used as a reference for assessing ELISA and CLIA reliability. Samples, separated into positive and negative LAC, were selected by CLIA detection in negative and positive IgG/IgM aCL and aβ2-GPI (cut-off > 20 U/mL). Results: The ELISA/CLIA comparison showed a 100% concordance in triple negative groups, highlighting an optimal analytical specificity; a higher concordance in the aβ2-GPI IgM-positive groups compared to positive aCL IgM (100% vs. 76% in LAC-positive groups; 82% vs. 71% in LAC-negative groups), as well as in aβ2-GPI IgM-negative groups compared to negative aCL IgM in LAC-positive groups (100% vs. 87.5%); and a massive concordance reduction in positive IgG aβ2-GPI and aCL groups (44% vs. 50% in LAC-positive groups; 4.8% vs. 4.5% in LAC-negative groups). Concordance increased in all groups with a higher CLIA cut-off (>50 U/mL). Conclusions: Although CLIA performances partly differed from ELISA, this does not preclude their use in APS diagnosis, which aims for higher sensitivity in detecting cases of disease. ELISA is confirmed to be more reliable for classification criteria that aim for high specificity to reduce false positives.