Background/Purpose: Antiphospholipid Syndrome (APS) is a systemic thromboinflammatory autoimmune disease characterized by thrombotic or obstetric events occurring in individuals with persistently positive antiphospholipid antibodies (aPL). Recently, research in adult populations has shown that antiphosphatidylserine/prothrombin antibodies (aPS/PT) are a reliable predictor of lupus anticoagulant (LA). These findings have yet to be reproduced in the pediatric population. We aim to ascertain the sensitivity, specificity, negative predictive value, and positive predictive value of aPS/PT to anticardiolipin (aCL), anti-beta-2 glycoprotein I (aβ2GPI), and LA in the pediatric population.

Methods: A retrospective chart review was performed of pediatric patients from 2019 to 2024 who had a full aPL panel (aPS/PT, aCL, aβ2GPI, LA) obtained as part of their medical evaluation for suspected or diagnosed conditions potentially related to aPL positivity. A cut-off of 40 units was used for aPL positivity for all antibodies. LA positivity was determined in accordance with international guidelines, and LA values obtained on anticoagulation were excluded. Sensitivities, specificities, negative predictive values, and positive predictive values were calculated with 95% confidence intervals.

Results: Our cohort included 298 patients who underwent aPL testing (Table 1). The majority of patients were female (72.4%), white (56.7%), and non-Hispanic (62.8%). Mean age at time of laboratory evaluation was 13.5 ± 4.3 years. Almost half (45%) of the cohort were diagnosed with a rheumatologic disease, most commonly systemic lupus erythematosus (n=89). Twelve patients (4%) had confirmed APS. Twenty patients with rheumatologic disease experienced at least one thrombotic event (Table 2). In the entire cohort, 30 patients (10.1%) had positive aPS/PT IgG and 56 (18.8%) had positive aPS/PT IgM (Table 1). Positive aPS/PT IgG and IgM showed high specificity (IgG 96.9%, 95%CI 94.0-98.4%; IgM 89.5%, 95%CI 85.1-92.7%) and low to moderate sensitivity (IgG 53.7%, 95%CI 38.8-67.9%; IgM 70.7%, 95%CI 54.0-80.9%) for LA positivity (Table 3). The negative predictive value of both aPS/PT IgG and IgM were high ( >90%) for LA, aCL, and aβ2GPI. Ten patients were triple positive for LA, aCL, and aβ2GPI, and aPS/PT IgG was highly specific (92.4%, 95%CI 88.7-94.9%) and moderately sensitive (80%, 95%CI 49.0-96.5%). Negative predictive value of aPS/PT IgG and IgM for triple positivity exceeded 99%.

Conclusion: Overall, the high specificity combined with the strong negative predictive values of aPS/PT IgG and IgM highlights the ability to use such antibodies to rule in the presence of LA and other aPL when positive and to confidently exclude them when negative. These findings align with previous adult literature and highlight the usefulness of aPS/PT as a predictor of lupus anticoagulant in the pediatric population. As anticoagulation can affect the interpretation of LA, positive aPS/PT, when associated with a positive LA, offers a useful alternative to monitor LA regardless of patients’ anticoagulation status. Additionally, with institutional variation in the conduct of LA, aPS/PT may provide a more comparable measure for multicenter research collaborations.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/analysis-of-antiphosphatidylserine-prothrombin-antibodies-as-a-predictor-of-lupus-anticoagulant-in-the-pediatric-population/