Background: Systemic lupus erythematosus (SLE) and antiphospholipid syndrome (APS) represent interconnected autoimmune disorders, closely associated in their development. Antiphospholipid antibodies (aPL) are detected in approximately 20-40% of SLE patients with a subsequent evolution to overt APS in 50-70% of them within 20 years. The recently published 2023 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) APS classification criteria [1] were commissioned to address the limitations of the 2006 revised Sapporo criteria. These novel, weighted, risk-stratified criteria encompass a broader spectrum of heterogenous APS manifestations and exhibit heightened specificity (99%). However, the 2023 ACR/EULAR APS classification criteria have not yet been validated in all possible subpopulations, e.g., aPL-positive SLE patients.

Objectives: to assess the performance characteristics of the 2023 ACR/EULAR APS classification criteria and the 2006 revised Sapporo criteria in Ukrainian cohort of aPL-positive SLE patients.

Methods: A total of 59 SLE patients (aged 37.1±12.0 years; 84.6% females) with positive aPL were enrolled. Lupus anticoagulant was determined by coagulation-based assay with 3-step procedure (screening-mixing-confirmation). Anticardiolipin and anti-β2-glycoprotein antibodies were measured by enzyme-linked immunosorbent assay (ELISA). Clinical and laboratory data relevant to the 2023 ACR/EULAR APS classification criteria and the 2006 revised Sapporo criteria were analyzed. If a clinical criterion was equally or more likely explained as attributable to SLE, it was not scored. Sensitivity and specificity with 95% confidence intervals (95% CI) were evaluated for both sets of criteria, each compared against consensus by two experienced independent rheumatologists as the “gold standard”. The level of agreement was assessed using Cohen’s kappa.

Results: In our cohort 30 patients (50.8%) were diagnosed with APS by rheumatologists’ consensus. Among them, 15 patients simultaneously fulfilled both the 2023 ACR/EULAR and the 2006 revised Sapporo criteria, 6 patients met only the 2023 ACR/EULAR criteria, 7 patients met only the 2006 revised Sapporo criteria, and 2 patients did not meet any criteria. The 2023 ACR/EULAR APS classification criteria demonstrated a specificity of 96.6% (95% CI 0.82-0.99), while the 2006 revised Sapporo criteria had a specificity of 86.2% (95% CI 0.68-0.96). The sensitivity of the 2023 ACR/EULAR criteria was 70.0% (95% CI 0.51-0.85), compared to a sensitivity of 73.3% (95% CI 0.54-0.88) using the 2006 Sapporo criteria. There was fair agreement (kappa 0.37, 95% CI 0.13-0.61) between the two sets of classification criteria. The new classification criteria showed substantial agreement with the established diagnosis of APS (kappa 0.66, 95% CI 0.47-0.85), while the reliability of Sapporo criteria was moderate (kappa 0.59, 95% CI 0.39-0.80).

Conclusion: The 2023 ACR/EULAR APS classification criteria exhibit superior specificity (96.6% vs 86.2%) and slightly lower sensitivity (70.0% vs 73.3%) when compared to the 2006 revised Sapporo criteria in aPL-positive SLE patients. Additionally, the new classification criteria demonstrate stronger agreement with the established diagnosis of APS than the Sapporo criteria (kappa 0.66 vs kappa 0.59).

REFERENCES: [1] Barbhaya M, et al. 2023 ACR/EULAR Antiphospholipid Syndrome Classification Criteria. Arthritis Rheumatol. 2023;75(10):1687-1702. doi: 10.1002/art.42624.

Acknowledgements: NIL.

Disclosure of Interests: None declared.