Semiquantitative interpretation of anticardiolipin and antiβ2glycoprotein I antibodies measured with various analytical platforms: Communication from the ISTH SSC Subcommittee on Lupus Anticoagulant/Antiphospholipid Antibodies

A. Vandevelde, W. Chayoua, B. de Laat, J.C. Gris, G.W. Moore, J. Musial, S. Zuily, D. Wahl, K.M.J. Devreese*

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review


Background Anti beta 2glycoprotein I (a beta 2GPI) and anticardiolipin (aCL) IgG/IgM show differences in positive/negative agreement and titers between solid phase platforms. Method-specific semiquantitative categorization of titers could improve and harmonize the interpretation across platforms. Aim To evaluate the traditional 40/80-unit thresholds used for aCL and a beta 2GPI for categorization into moderate/high positivity with different analytical systems, and to compare with alternative thresholds. Material and methods aCL and a beta 2GPI thresholds were calculated for two automated systems (chemiluminescent immunoassay [CLIA] and multiplex flow immunoassay [MFI]) by receiver operating characteristic curve analysis on 1108 patient samples, including patients with and without antiphospholipid syndrome (APS), and confirmed on a second population (n = 279). Alternatively, regression analysis on diluted standard material was applied to identify thresholds. Thresholds were compared to 40/80 threshold measured by an enzyme-linked immunosorbent assay (ELISA). Additionally, likelihood ratios (LR) were calculated. Results Threshold levels of 40/80 units show poor agreement between ELISA and automated platforms for classification into low/moderate/high positivity, especially for aCL/a beta 2GPI IgG. Agreement for semiquantitative interpretation of antiphospholipid antibodies (aPL) IgG between ELISA and CLIA/MFI improves with alternative thresholds. LR for aPL IgG increase for thrombotic and obstetric APS based on 40/80 thresholds for ELISA and adapted thresholds for the other systems, but not for IgM. Conclusion Use of 40/80 units as medium/high thresholds is acceptable for aCL/a beta 2GPI IgG ELISA, but not for CLIA and MFI. Alternative semiquantitative thresholds for non-ELISA platforms can be determined by a clinical approach or by using monoclonal antibodies. Semiquantitative reporting of aPL IgM has less impact on increasing probability for APS.
Original languageEnglish
Pages (from-to)508-524
Number of pages17
JournalJournal of Thrombosis and Haemostasis
Issue number2
Early online date2 Dec 2021
Publication statusPublished - Feb 2022


  • antiphospholipid antibodies
  • classification
  • immunoassay
  • risk
  • thresholds

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