Background:While there have been advances in the therapy of systemic lupus erythematosus (SLE) in recent years, there have been no major new findings in SLE biomarkers [1, 2]. Type I interferon (IFN) plays a pivotal role in the pathogenesis of SLE [3]. In 2008, we first described CD169 / SIGLEC-1 (sialic acid-binding immunoglobulin-like lectin-1), an interferon-induced adhesion molecule on monocytes in SLE patients [4]. For over five years SIGLEC-1 has been routinely assessed in our clinic.Objectives:To evaluate and compare the diagnostic utility of the type I IFN induced SIGLEC-1 with established biomarkers in the initial diagnosis of the disease.Methods:We analyzed retrospectively 232 patients who were on suspicion of SLE at Charité University Hospital Berlin between October 2015 and September 2020. Patients underwent full clinical characterization, and biomarkers were determined in the routine laboratory. Based on the final diagnosis, we divided patients into two groups: A) initial diagnosis of SLE and B) Non-SLE mimicking condition.Results:In 76 patients (32.3 %) SLE was confirmed by fulfilling the EULAR / ACR 2019 classification criteria [5]. SIGLEC-1 was dramatically increased in patients with an initial diagnosis of SLE compared to patients without SLE (p<0.0001). For a threshold of 2500 molecule per monocyte, a sensitivity of 98.7 %, a specificity of 82.1 %, a negative predictive value (NPV) of 99.2 %, and a positive predictive value (PPV) of 72.8 % were calculated for SIGLEC-1. Adjusted to the prevalence of SLE in Germany (36.7 per 100,000 inhabitants [6]) NPV and PPV turned out to > 99.9 % and 0.2 %. We further aimed to compare not only the performance of the tests at a given cutoff but also across all possible measured values. Therefore, we conducted ROC curves analyses (see figure 1). The area under the curve (AUC) of SIGLEC-1 test was significantly higher than that of ANA test (AUC=0.88, p=0.031), C3 (AUC = 0.83, p=0.001), C4 (AUC=0.83, p=0.002), but not than that of the Anti-dsDNA ELISA (AUC=0.90, p=0.163).Conclusion:Our study shows that IFN activity is a hallmark at the onset of the disease and that the interferon biomarker SIGLEC-1 is valuable to rule out SLE in suspected cases.References:[1]Ostendorf L, Burns M, Durek P, Heinz GA, Heinrich F, Garantziotis P, Enghard P, Richter U, Biesen R, Schneider U et al: Targeting CD38 with Daratumumab in Refractory Systemic Lupus Erythematosus. N Engl J Med 2020, 383(12):1149-1155.[2]Furie R, Rovin BH, Houssiau F, Malvar A, Teng YKO, Contreras G, Amoura Z, Yu X, Mok CC, Santiago MB et al: Two-Year, Randomized, Controlled Trial of Belimumab in Lupus Nephritis. N Engl J Med 2020, 383(12):1117-1128.[3]Ronnblom L, Leonard D: Interferon pathway in SLE: one key to unlocking the mystery of the disease. Lupus Sci Med 2019, 6(1):e000270.[4]Biesen R, Demir C, Barkhudarova F, Grun JR, Steinbrich-Zollner M, Backhaus M, Haupl T, Rudwaleit M, Riemekasten G, Radbruch A et al: Sialic acid-binding Ig-like lectin 1 expression in inflammatory and resident monocytes is a potential biomarker for monitoring disease activity and success of therapy in systemic lupus erythematosus. Arthritis Rheum 2008, 58(4):1136-1145.[5]Aringer M, Costenbader K, Daikh D, Brinks R, Mosca M, Ramsey-Goldman R, Smolen JS, Wofsy D, Boumpas DT, Kamen DL et al: 2019 European League Against Rheumatism/American College of Rheumatology classification criteria for systemic lupus erythematosus. Annals of the Rheumatic Diseases 2019, 78(9):1151-1159.[6]Brinks R, Fischer-Betz R, Sander O, Richter JG, Chehab G, Schneider M: Age-specific prevalence of diagnosed systemic lupus erythematosus in Germany 2002 and projection to 2030. Lupus 2014, 23(13):1407-1411.Disclosure of Interests:None declared
POS0706 PERFORMANCES OF DIFFERENT CLASSIFICATION CRITERIA FOR SYSTEMIC LUPUS ERYTHEMATOSUS IN A SINGLE CENTER COHORT FROM TURKEY