The 2023 American College of Rheumatology (ACR)/European Alliance of Associations for Rheumatology (EULAR) antiphospholipid syndrome (APS) classification criteria incorporate more clinical items and use weighted items with the aim of classifying APS with increased specificity.¹ The new criteria has been validated in two cohorts, but none of the patients and centers are from Asian populations. To evaluate the performance of the new classification criteria in Chinese patients with APS, we conducted a study consisting of 427 suspected patients from the Antiphospholipid Syndrome Chinese Collaborative (APSCC) cohort, including two cohorts from the Peking University People's Hospital (PKUPH) and Peking University Third Hospital. The study was approved by the Ethics Committee of PKUPH. Among them, 256 patients were clinically diagnosed with APS by our experienced rheumatologists (YG and CL). Of the diagnosed patients, 167 were classified as having thrombotic APS, whereas 41 were classified as having obstetric APS.

Compared with 2006 Sapporo criteria², the 2023 ACR/EULAR criteria exhibited a lower sensitivity (78% vs 87%) but higher specificity (98% vs 92%) for patients with overall APS. The area under the curve for the new criteria is similar to that of the 2006 criteria (0.880, 95% confidence interval [CI] 0.846–0.914, vs 0.895, 95%CI 0.861–0.928, P = 0.2617). However, for patients with obstetric APS, the sensitivity was markedly lower (56% vs 93%), with a slightly higher specificity (100% vs 92%; Table 1). Furthermore, compared with 199 patients with APS (77.7%) who met the criteria, 57 patients with APS (22.3%) who did not meet the criteria showed a higher percentage of overall pregnancy morbidity (52.5% vs 29.4%, P = 0.005) and a lower percentage of macrovascular thrombosis events (22.8% vs 87.4%, P < 0.001; Table 2). This may be partially due to the fact that patients with APS who have experienced fetal loss without other severe features were assigned only a score of 1. As seen in our cohorts, patients who did not meet the criteria showed a higher percentage of more than one early fetal death at 10 to 16 weeks (19% vs 5%, P = 0.028), and they did not meet the criteria, perhaps partially due to a lower clinical domain score. Besides, adding single-once positivity of lupus anticoagulant (LAC) as a laboratory characteristic did not appear to enhance the sensitivity. Our patients with APS who did not meet the criteria had a higher percentage of single-once LAC positivity (52.6% vs 8.5%, P < 0.05).

Absent a definitive gold standard, establishing a classification system for patients with APS can be a challenge, especially for patients with obstetric APS. Although the 2023 criteria redefined pregnancy morbidity, they still did not demonstrate a stronger power in APS classification. Meanwhile, several studies on patients with “noncriteria” obstetric APS have suggested that eliminating less strict clinical and laboratory parameters may result in missing diagnoses of obstetric APS.³ These findings prompt questions about accurate diagnosis and the appropriateness of initiating treatment in Chinese patients with pure obstetric APS, which should be the focus of further research.

Supported by Peking University People's Hospital Research and Development Funds (grant RDJP2022-12) and Peking University Clinical Scientist Training Program (BMU2023PYJH010). Yuzhou Gan's work was partially supported by Michigan Medicine and Peking University Health Science Center Joint Institute for Clinical and Translational Research.