Evaluation of a new set of automated chemiluminescense assays for anticardiolipin and anti-beta2-glycoprotein I antibodies in the laboratory diagnosis of the antiphospholipid syndrome

Abstract Introduction The laboratory diagnosis of antiphospholipid syndrome (APS) requires the demonstration of antiphospholipid antibodies (aPL): lupus anticoagulant (LAC) measured through coagulation assays, anticardiolipin IgG or IgM antibodies (aCL) and/or anti-β2glycoprotein I IgG or IgM antibodies (aβ2GPI), usually detected by ELISA Materials and methods We evaluated the diagnostic value of aCL and aβ2GPI measured by a new automated system using the chemiluminescence principle, the immunoanalyzer Zenit RA (Menarini). Results Results of aCL and aβ2GPI were correlated with the clinical background of the patients and with results of ELISA (n=314). Correlated to the clinical background sensitivity/specificity ranged for aCL IgG between 7.5-45.2% / 54.2-98.8%, for aCL IgM 3.4-5.5% / 89.9-94%, for aβ2GPI IgG 5.5-25.3% / 75.6-100% and aβ2GPI IgM 3.4-4.8% / 89.9-92.3%, depending on the cut-off used. Sensitivity with manufacturer's cut-offs was comparable to ELISA, except for aβ2GPI IgG with a significantly lower sensitivity compared to ELISA (5.5% vs 11.6%). In the APS patient population (n=30) sensitivity of aCL IgG and aβ2GPI IgG was higher measured by ELISA compared to Zenit RA (46.7% vs 30.0%, and 46.7% vs 26.7%, respectively). Agreement between Zenit RA results and ELISA results for the four parameters was moderate (Kappa-values ranging 0.509-0.565). Sensitivity was 38.5%, 53.3%, 40% and 69.2% for aCL IgG, aCL IgM, aβ2GPI IgG and aβ2GPI IgM, respectively, applying the highest cut-off value for Zenit RA, raising towards 64.3%, 100%, 57.1%, for aCL IgG, aCL IgM, aβ2GPI IgG, respectively, in a APS patient population. Conclusions The new technology of chemiluminescense for measuring aPL showed good performance characteristics. Interpretation of results with a cut-off value associated with a good discrimination for disease, resulted in a lower sensitivity for the diagnosis of APS for aβ2GPI IgG measured by Zenit RA assays compared to ELISA; sensitivity for aCL IgG was comparable to ELISA. Specificity for all parameters was high and comparable for aCL and aβ2GPI.