Anti-phosphatidylserine prothrombin antibodies as a predictor of the lupus anticoagulant in an all-comer population

Background: Anti-phosphatidylserine prothrombin antibodies (aPSPT) are reported to be highly associated with the lupus anticoagulant (LAC) in established antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE) cohorts. Further, aPSPT has been suggested to be a useful surrogate LAC marker. However, validation studies replicating this relationship in an all-comer study population in the diagnostic clinical setting are lacking. Objectives: To determine the sensitivity and specificity of aPSPT to the LAC in an all-comer population undergoing evaluation for suspected APS. Methods: An assembled cross-sectional cohort from June 2017 to December 2018 undergoing APS evaluations across all medical specialties were reviewed for LAC, aPSPT, anti-cardiolipin (aCL), and anti-β2 glycoprotein-1 (β2GP1). Sensitivities, specificities, and negative and positive predictive values were calculated. Results and Conclusions: A cohort of 166 eligible patients was identified. Seventy-one percent were female, 89% White, 15% with SLE, and 21% with APS. The aPSPT was found to be the most specific to the LAC. Specificity of IgG aPSPT was 100% (96%–100%) and IgM aPSPT was 97% (91%–100%) to the LAC. Corresponding positive predictive value for IgG aPSPT was 100% (89%–100%) and IgM aPSPT was 95% (84%–99%). In contrast, the sensitivities of aPSPT to the LAC were less robust, only in the 40%–50% range. The findings validate previously reported findings and lends extension to an all-comer population. These findings corroborate aPSPT as a potentially useful clinical marker of the LAC.