Serology and Scores

The presence of anti-cardiolipin (aCL) and anti-β₂‐glycoprotein I (aβ₂GPI) of the IgG and IgM isotypes was measured by enzyme‐linked immunosorbent assay (ELISA) or by a multiplex system. The kits that were used were all commercial (ELISA—aB2GPI by AESKU Diagnostics (Wendelsheim, Germany) and aCL by Varelisa (Pharmacia Diagnostics, Stockholm, Sweden); Bioplex both aB2GPI and aCL by Bio-Rad, Hercules, CA, USA). B2GPI and ACL were considered positive if antibody levels were above 20 MPL units (IgG phospholipid units or IgM phospholipid units), or if >99th percentile or according to the manufacturer’s instructions were present in a minimum of two tests performed at least 12 weeks apart were obtained. Very high titers were considered as fourfold or higher of the upper normal limit as specified for each kit. Lupus anticoagulant (LA) activity was detected by coagulation assays in routine use at each center and was consistent with the International Society of Thrombosis and Hemostasis guidelines (18). The LA assays were modified in 2016; up until 2016, LA activity was measured by LA-responsive activated partial thromboplastin time (aPTT) aPL (by Stago, confirmed using the Actem FS Kit by Siemens, Erlangen, Germany), and from 2016, LA activity was measured by a combination of silicon clotting time and the use of the Russell Viper Venom Kit (by IL, Bedford, MA, USA). In case of anticoagulation treatment or spontaneous INR >1.5, patients’ plasma was mixed with normal plasma in order to reduce false positivity. Positivity was defined as single, double, or triple positive according to the number of different positive tests obtained.

In this study, we used the validated aGAPSS (11, 19) which allots 3 points for dyslipidemia, 1 for arterial hypertension, 5 for anti-cardiolipin antibodies IgG/IgM, 4 for anti-β2 glycoprotein IgG/IgM, and 4 for lupus anticoagulant. Catastrophic APS (cAPS) was defined according to the International Task Force on CAPS criteria (2).