Avoiding misclassification of thrombotic primary antiphospholipid syndrome as systemic lupus erythematosus (SLE): What are the best-performing SLE classification criteria?

Background Systemic lupus erythematosus (SLE) and Primary Antiphospholipid Syndrome (PAPS) overlap clinical and immunological features. Therefore, misclassification of PAPS patients as SLE is a concern. The ACR/EULAR 2019 SLE classification has never been studied in PAPS. Objective To verify if the ACR/EULAR 2019 SLE classification can correctly classify a PAPS patient as not having SLE and compare its performance with the SLICC 2012 SLE classification. Methods: One-hundred thrombotic PAPS patients who fulfilled the Sidney criteria were consecutively screened and those who attended the inclusion criteria were submitted to ACR/EULAR 2019 and SLICC 2012 classifications. Results Sixty-seven PAPS patients were included in this study. The majority was female (89.6%) with median age at study inclusion of 45 years (35–53) and median PAPS disease duration of 13 years (8–19). PAPS correct classification was observed more often with ACR/EULAR 2019 than SLICC 2021 criteria (94.0% vs. 64.2%; p Conclusion ACR/EULAR 2019 had high accuracy for distinguishing PAPS from SLE, whereas the SLICC 2012 incorrectly classified more than one third of the PAPS patients as having SLE.