Validation of the global antiphospholipid syndrome score by adding anti-domain-i antibodies and İGA isotypes of antiphospholipid antibodies within the antiphospholipid syndrome (APS) classification criteria

Objectives: Vascular thrombosis (VT) is the leading cause of mortality in antiphospholipid syndrome (APS). In this cross-sectional study, we aimed to evaluate the validity of a score developed by adding anti-domain-I (aDI) and IgA isotypes of antiphospholipid antibodies (aPL) to the global APS score (GAPSS) in predicting thrombosis and other clinical manifestations of APS. Patients and Methods: Fifty patients with primary APS, 68 patients with APS secondary to systemic lupus erythematosus (SLE) and 52 patients with aPL(+) SLE were classified as VT, pregnancy morbidity (PM), VT+PM or aPL(+) SLE. Anticardiolipin (aCL), anti-β2-glycoprotein I (aβ2GPI), aDI IgG/IgM/IgA and anti-phosphotidylserine/prothrombin (aPS/PT) IgG/IgM were detected by ELISA and LA was measured by dRVVT and aPTT. The GAPSS and aGAPSS were calculated for each patient as previously defined. ITF-GAPSS were developed by assigning new regression coefficients to components of the GAPSS by multivariate regression analysis and ITF-GAPSS-2 by adding aDI IgG/IgM/IgA, aCL IgA and aβ2GPI IgA to the analysis. Results: VT (n=71), PM (n=13) and VT+PM (n=34) groups had higher mean GAPSS and aGAPSS compared to aPL(+) SLE (n=52) (GAPSS P <0,001, P=0,007, P <0,001, respectively; aGAPSS P<0,001, P=0,005, P<0,001, respectively). Within VT (±PM), patients with recurrent thrombosis (n=43) and arterial thrombosis (n=72) had higher aGAPSS (P=0.008, P<0.001, respectively). While the mean ITF-GAPSS of VT and VT+PM were higher than the aPL(+) SLE (P=0.029, P=0.002, respectively), there was no difference between PM and aPL(+) SLE (P=0.432). There was no difference between the ITF-GAPSS-2 values of the four groups (P=0.471). The optimal GAPSS, aGAPSS, ITF-GAPSS and ITF-GAPSS-2 cut-off values for both APS diagnosis and thrombosis were calculated as ≥13, ≥10, 11 and ≥22, respectively. Conclusions: The GAPSS and aGAPSS successfully predict the risk of developing APS in aPL(+) patients. Adding aDI and IgA isotypes of aPLs decreases the predictive value of the score. The possible explanation of this is high prevalance of aDI and IgA aPL positivity in SLE patients, which may be related to disease activity (This study was funded by Istanbul University with the project number TTU-2019-33932).