#6-08E. Biomarkers or Epiphenomena? APC Resistance in Antiphospholipid Syndrome (Rheumatology, 2026)

Whether acquired activated protein C resistance (APCr) and anti-protein C antibodies predict future thrombosis in antiphospholipid antibody (aPL) carriers remains uncertain. Analyzing 370 aPL-positive patients, this prospective APS ACTION registry study demonstrated that while APCr and anti-protein C antibodies were highly prevalent—especially in high-risk phenotypes—neither biomarker independently predicted prospective thrombotic events, though small event numbers and baseline anticoagulation limit statistical power. These findings advise clinicians against using APCr or anti-protein C testing for routine thrombotic risk stratification in everyday practice.

Citation: Tohidi-Esfahani I, Venturelli V, Tektonidou M, et al. Prevalence and prognostic value of activated protein C resistance and anti-protein C antibodies in patients with aPLs: an APS ACTION Registry study. Rheumatology. 2026. DOI: 10.1093/rheumatology/keag304

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