Arne Vandevelde1,2, Walid Chayoua3,4, Bas de Laat3,4, Jean-Christophe Gris5,6, Gary W Moore7,8,9, Jacek Musiał10, Stéphane Zuily11, Denis Wahl11, Katrien M J Devreese1,2. 1. Coagulation Laboratory, Ghent University Hospital, Ghent, Belgium. 2. Department of Diagnostic Sciences, Ghent University, Ghent, Belgium. 3. Synapse Research Institute, Maastricht, the Netherlands. 4. Cardiovascular Research Institute Maastricht, Maastricht University Medical Centre, Maastricht, The Netherlands. 5. Centre Hospitalier Universitaire de Nîmes et Université de Montpellier, UMR UA11 INSERM Université de Montpellier IDESP, Montpellier, France. 6. Ivan Sechenov First Moscow State Medical University, Moscow, Russia. 7. Department of Haemostasis and Thrombosis, Viapath Analytics, Guy's & St. Thomas' Hospitals, London, UK. 8. Department of Haematology, Specialist Haemostasis Unit, Cambridge University Hospitals NHS Foundation Trust, Cambridge, UK. 9. Faculty of Science and Technology, Middlesex University, London, UK. 10. Department of Internal Medicine, Jagiellonian University Medical College, Kraków, Poland. 11. Vascular Medicine Division and Regional Competence Center for Rare Vascular and Systemic Autoimmune Diseases, Centre Hospitalier Regional Universitaire de Nancy, Université de Lorraine, Inserm, DCAC, Nancy, France.
Abstract
BACKGROUND: Antiβ2glycoprotein I (aβ2GPI) 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 aβ2GPI for categorization into moderate/high positivity with different analytical systems, and to compare with alternative thresholds. MATERIAL AND METHODS: aCL and aβ2GPI 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/aβ2GPI 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/aβ2GPI 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.
BACKGROUND: Antiβ2glycoprotein I (aβ2GPI) 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 aβ2GPI for categorization into moderate/high positivity with different analytical systems, and to compare with alternative thresholds. MATERIAL AND METHODS: aCL and aβ2GPI 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/aβ2GPI 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/aβ2GPI 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.