[Value of IgA antiphospholipid antibodies in diagnosis of the antiphospholipid syndrome].

Objective: To examine the prevalence of multiple antiphospholipid antibodies (aPL) subtypes in healthy people and antiphospholipid syndrome (APS) patients, and to assess the value of IgA-aPL in the diagnosis of APS. Methods: According to the 2006 Sydney International APS Classification Criteria, a total of 218 APS patients who were admitted to Peking Union Medical College Hospital or West China Hospital of Sichuan University from July to December 2019 were enrolled. Among them, 66 were males, and 152 were females, aged (44.5±15.4) years, including 148 primary APS patients and 70 secondary APS patients. Age-and gender-matched controls were collected at the same period at the ratio of 1∶1 with the APS cases. IgA/IgG/IgM anticardiolipin antibodies (aCL) and anti-ß2 glycoprotein I antibodies (aß2GPI) were detected by chemiluminescent immunoassay. The differences of indicators between groups were analyzed, and the receiver operating characteristic (ROC) curve was used to evaluate the diagnostic value of IgA-aPL for APS. Results: The positivity of IgA-aCL and IgA-aß2GPI was 20.6% and 15.6% in the APS patients, while in the IgG/IgM-aCL or IgG/IgM-aß2GPI negative individuals, the isolated positivity of IgA-aCL and IgA-aß2GPI was only 2.3% and 0.9%, respectively. Accordingly, IgA-aCL and IgA-aß2GPI isolated positivity could be used to diagnose APS (P=0.216, 1, respectively). The area under the ROC curve (AUC) of IgG/IgM-aCL for APS diagnosis was 0.833, which was significantly better than that of IgG-aCL alone (AUC=0.776, P<0.001); while the AUC of IgA/IgG/IgM-aCL was 0.833, which could not further increase the diagnostic value for APS (P=0.287). As for aß2GPI, the diagnostic efficacy of combined IgG/IgM (AUC=0.875) or IgA/IgG/IgM (AUC=0.875) antibodies was not superior to IgG-aß2GPI used alone (AUC=0.869, both P>0.05). Besides, patients with IgA-aPL were more likely to have heart valve lesions and thrombocytopenia (both P<0.05). Conclusion: Based on the existing serological markers, such as lupus anticoagulant, IgG/IgM subtype of aCL and aß2GPI, testing IgA-aCL and IgA-aß2GPI cannot further improve the predictive value of APS. However, IgA-aPL is associated with clinical manifestations of APS, including heart valve lesions and thrombocytopenia.