Study of Clinical Utility of Antibodies to Phosphatidylserine/prothrombin Complex in Asian-Indian Patients with Suspected APS

Antiphospholipid syndrome (APS) is the most common acquired pro-thrombotic disorder, also associated with obstetric complications. Phosphatidylserine/Prothrombin complex antibody (aPSPT) though associated with various APS manifestations, is not included in the revised Sapporo Criteria. To study the prevalence of aPSPT in Asian-Indian patients with suspected APS and compare its performance with the criteria anti-phospholipid antibodies (APLs). Electronic charts of 372 individuals whose sera was tested for aPSPT in suspected APS between June 2014 and May 2016 were retrieved and analyzed. aPSPT was assayed by ELISA. aPSPT tested individuals were categorized into cases-seropositive and seronegative APS (SNAPS) and controls. aPSPT was positive in 24/58 (41.3%) cases and 17/314 (5.4%) controls (p < 0.001). aPSPT positivity was seen in 44.5%, 38.7%, and 58.4% in primary, secondary and SNAPS patients respectively. aPSPT had the best performance among all APLs, in obstetric APS with 31% sensitivity, 97.7% specificity, and an odds ratio of 18.8. It showed 41.4% sensitivity, 94.6% specificity for the classification/diagnosis of primary APS and 38.7% sensitivity, 91.5% specificity for secondary APS. Addition of aPSPT to current APS criteria to SNAPS patients led to reclassification of additional 12.1% patients as APS overall and 42.8% in obstetric APS category. In Asian-Indian patients with suspected APS, aPSPT outperformed all classical APLs in diagnosis/classification of obstetric APS and both isotypes of beta 2-glycoprotein-I antibodies in diagnosis/classification of APS. aPSPT could reclassify additional 12.1 and 42.8% patients as APS overall and obstetric APS respectively, over and above the cases satisfying revised Sapporo criteria.