Pos0766 the role of antibodies to the phosphatidylserine/prothrombin complex in the diagnosis of antiphospholipid syndrome

BackgroundThe study of other non-criteria antiphospholipid antibodies (aPL) may improve the stratification of patients with antiphospholipid syndrome (APS) and assist in the interpretation of conflicting results on aPL testing.ObjectivesTo determine the significance of antibodies to the phosphatidylserine/prothrombin complex (anti-PS/PT) in patients with systemic lupus erythematosus (SLE) and APS.MethodsThe study included 190 patients who signed informed consent, aged 37,0 [29,0-44,0] years and disease duration 7,0 [2,0-15,0] years. Male/female ratio was 44 (23)/146 (77). 123 (64,7%) of 190 patients had reliable SLE and 55 (29%) had PAPS. The control group was left with 100 relatively healthy, age-matched individuals. Classical aPL (IgG/IgM-aCL, IgG/IgM-αβ2-GP1, LA) were meassured at two time points separated by at least 12 weeks in all patients included in this study. IgG/IgM anti-PS/PT was determined by enzyme immunoassay (ELISA) using a Tecan sunrise absorbance microplate spectrophotometer (Austria) with an AESKULISA Serin-Prothrombin-GM antibody reagent kit. IgG/IgM anti-PS/PT were measured in U/ml. Values >18 U/ml were considered positive. The range of measurements was: 1 to 300 U/ml.ResultsIn 144 (76%) of 190 patients were revealed IgG anti-PS/PT, 55 (29%) - IgM anti-PS/PT, a combination of IgG anti-PS/PT and IgM anti-PS/PT was found in 53 (28%). IgG anti-PS/PT and IgM anti-PS were detected in 39 of the 70 (56%) remaining patients who were negative for criterion aPL. The median IgG anti-PS/PT was 101.2 U/ml [31,0-180,5] in patients with APS and was significantly higher than 23,7 [14,1-49,8] U/ml in patients without APS and controls. IgM anti-PS/PT levels in patients with and without APS were comparable. Thrombosis was significantly more common in patients with IgG anti-PS/PT: 95 (81,2%) of 117 patients with thrombosis compared with patients negative for IgG anti-PS/PT (22 (18,8%) of 46 patients) (χ2=4,85; P=0,03). Arterial, but not venous thrombosis, was associated with IgG anti-PS/PT positivity. IgG anti-PS/PT was detected in 53 (88,3%) of 60 patients with arterial thromboses, and in 7 (11,7%) of 46 patients of IgG anti-PS/PT negative. The incidence of thrombocytopenia in the SLE+APS patient group was associated with the presence of IgG anti-PS/PT, which was detected in 18 of 19 patients, versus 6 of 12 in SLE without aPL (P<0,007). In the other patient groups, the frequency of thrombocytopenia and IgG anti-PS/PT positivity was not statistically significant. The frequency of anti-PS/PT detection was independent of LA positivity. IgG and/or IgM anti-PS/PT were detected in 26 (87%) of 30 patients positive for LA and in 21 (78%) of 27 patients LA negative. (P<0,05). The sensitivity of anti-PS/PT IgG for APS was 85%, specificity - 64%, the sensitivity of anti-PS/PT IgM was lower - 35%, but higher specificity - 88%.ConclusionThe frequency of anti-PS/PT detection in the examined patients was high: 76% had IgG anti-PS/PT, 29% - IgM anti-PS/PT and 28% - a combination of them. The levels of IgG anti-PS/PT were significantly higher in patients with APS compared to patients without APS and controls. IgM anti-PS/PT values in patients with and without APS were comparable but higher compared to controls. Thrombosis was associated with IgG anti-PS/PT positivity. Arterial thrombosis was significantly more frequent in patients with IgG anti-PS/PT (χ2=4,85; P=0,006). The sensitivity of IgG anti-PS/PT for APS was 85%, and specificity was 64%; IgM anti-PS/PT had a lower sensitivity of 35%, but a higher specificity of 88%.The study was performed at the V.A. Nasonova Research Institute of Rheumatology within the framework of the fundamental topic FURS-2022-003.Disclosure of InterestsNone declared