The aims of this prospective cross-sectional study were to a) evaluate the prevalence of APCr in APS patients and SLE patients compared to non-APS/SLE thrombotic controls using the ST-Genesia® system in the presence/absence of TM and b) to compare APCr with the CAT system (using recombinant human APC (rh-APC) and Protac®) to establish if both systems can detect APCr observed in APS and SLE patients. Here, APC is linked to systemic lupus erythematosus.