SAT0204 COMPARING OCCURRENCE AND CLINICAL SIGNIFICANCE OF ANTI-PHOSPHOLIPID AUTOANTIBODIES AMONG SUDANESE AND SWEDISH SLE PATIENTS USING CONVENTIONAL AND NATION-BASED CUTOFFS
Authors: S. Elbagir, A. Elshafie, E. M. Elagib, N. A. Mohammed, V. A. Manivel, E. Pertsinidou, M. A. M. Nur, I. Gunnarsson, E. Svenungsson, J. Rönnelid
Journal: Annals of the Rheumatic Diseases (2020)

Background: Antiphospholipid antibodies (aPL) of IgA isotype are prevalent in SLE patients of African-American, Afro-Caribbean and South-African origin, but data from North Africa are lacking Objectives: To compare and determine clinical significance of aPL isotypes in Sudanese and Swedish SLE patients using nation-based cutoffs Methods: Consecutive Sudanese (n=115) and Swedish (n=340) SLE patients and 106 and 318 age- and sex-matched national controls were included. All patients fulfilled the 1982 ACR SLE classification criteria. IgA/G/M anti-cardiolipin and anti-β 2 GPI were analyzed with two independent assays (Fluorescence Enzyme Immuno Assay (FEIA) from Thermo Fisher Scientific and Particle-based Multi-Analyte Technology (PMAT) from Inova Diagnostics). IgA anti-β 2 GPI domain1 (D1) was investigated with chemiluminescence (CIA), Inova Diagnostics. APS-related events were obtained from patients’ records. Manufacturers’, 95 th and 99 th percentile cutoffs, based on national controls calculated by non-parametric methods, were used Results: Sudanese patients had higher levels and prevalence of IgA aPL using manufacturers’ cutoffs (Table 1 and Figure 1). IgA/IgG aPL were also higher among Sudanese controls, But, Swedish patients were more often positive for IgA anti-β 2 GPI with both assays when national cutoffs were applied (Table 1). Occurrence of IgA anti-D1 did not differ between the countries. Venous thromboses were less common among Sudanese patients and no aPL, including IgA anti-β 2 GPI associated with thrombosis in Sudanese patients. Thrombosis in Swedes associated with IgG/IgM aPL. Fetal loss associated with aPL in both cohorts most evident after national adjustments Table 1. FEIA Sudan n=92 FEIA Sweden n=291 P PMAT/CIA Sudan n=93 PMAT/CIA Sweden n=333 P IgA CL median/IQR 6.5/5.2 4.0/4.1 &lt;0.0001 194/185 148/112 &lt;0.0001 IgG CL 4.1/5.1 3.0/4.5 0.0002 205/137 190/215.1 0.09 IgM CL 2.7/6.8 3.7/5.4 0.02 214/251.5 193/3502 0.2 IgA β2GPI 6.3/14.2 2.7/3.8 &lt;0.0001 212/347 118/152 &lt;0.0001 IgG β2GPI 4.2/2.9 1.8/2.3 &lt;0.0001 158/110.7 145.2/147.5 0.04 IgM β2GPI 2.0/3.0 1.4/2.2 0.006 146.2/189.7 132.5/235.4 0.09 IgA B2GP1 D1 1542/1253.5 1683/1518.1 0.045 IgA CL common cutoff n(%) 9(9.8) 17(5.8) 0.2 32(35.2) 75(22.7) 0.02 IgG CL 4(4.3) 21(6.7) 0.4 14(15) 72(22.1) 0.1 IgM CL 3(3.2) 14(4.5) 0.6 10(11.4) 43(13.1) 0.6 IgA β2GPI 32(34.8) 43(14.9) &lt;0.0001 38(41.8) 76(23) 0.0004 IgG β2GPI 10(10.9) 44(14.1) 0.4 5(5.4) 50(15.3) 0.01 IgM β2GPI 10(10.9) 27(8.7) 0.5 12(13.6) 42(12.9) 0.8 IgA B2GP1 D1 6(6.4) 38(11.4) 0.2 IgA CL 95 th cutoff n(%) 9(9.8) 54(18.6) 0.047 36(39.6) 121(26.6) 0.6 IgG CL 8(8.7) 42(13.5) 0.2 24(25.8) 103(31.6) 0.3 IgM CL 8(8.7) 39(12.5) 0.3 16(18.2) 47(14.4) 0.4 IgA β2GPI 18(19.6) 100(34.7) 0.006 20(22) 125(37.8) 0.005 IgG β2GPI 2(2.1) 67(21.5) &lt;0.0001 19(20.4) 83(25.5) 0.3 IgM β2GPI 14(15.22) 57(18.3) 0.5 20(22.7) 57(17.5) 0.3 IgA B2GP1 D1 25(26.9) 69(20.7) 0.2 Figure 1. Conclusion: IgA anti-β 2 GPI levels were generally higher among Sudanese compared to Swedish SLE patients and controls, but after national adjustments more Swedish than Sudanese patients were positive. IgA anti-D1 was not increased in Sudanese patients. Previous studies on populations of African-origin, which demonstrate high prevalence of IgA aPL positivity, should be re-evaluated using similar cutoff approach Acknowledgments: : We thank Maryam Poorafshar at Thermo Fischer Scientific and Silvia Casas and Michael Mahler at Inova Diagnostics for help with analyses Disclosure of Interests: None declared