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.

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.