Comparison of Acquired Activated Protein C Resistance, Using the CAT and ST-Genesia Analysers and Three Thrombin Generation Methods, in APS and SLE Patients.

Background: Acquired activated protein C resistance (APCr) has been identified in antiphospholipid syndrome (APS) and systemic lupus erythematosus (SLE).

Objective: To assess agreement between the ST-Genesia and CAT analysers in identifying APCr prevalence in APS/SLE patients, using three thrombin generation (TG) methods.

Methods: APCr was assessed with the ST-Genesia using STG-ThromboScreen and with the CAT using recombinant human activated protein C and Protac in 105 APS, 53 SLE patients and 36 thrombotic controls. Agreement was expressed in % and by Cohen's kappa coefficient.

Results: APCr values were consistently lower with the ST-Genesia compared to the CAT, using either method, in both APS and SLE patients. Agreement between the two analysers in identifying APS and SLE patients with APCr was poor (≤65.9%, ≤0.20) or fair (≤68.5%, ≥0.29), regardless of TG method, respectively; no agreement was observed in thrombotic controls. APCr with both the ST Genesia and the CAT using Protac, but not the CAT using rhAPC, was significantly greater in triple antiphospholipid antibody (aPL) APS patients compared to double/single aPL patients ( < 0.04) and in thrombotic SLE patients compared to non-thrombotic SLE patients ( < 0.05). Notably, the ST-Genesia, unlike the CAT, with either method, identified significantly greater APCr in pregnancy morbidity (median, confidence intervals; 36.9%, 21.9-49.0%) compared to thrombotic (45.7%, 39.6-55.5%) APS patients ( = 0.03).

Conclusion: Despite the broadly similar methodology used by CAT and ST-Genesia, agreement in APCr was poor/fair, with results not being interchangeable. This may reflect differences in the TG method, use of different reagents, and analyser data handling.