Background/Purpose: The current recommended anti-thrombotic therapy for patients with anti-phospholipid syndrome (APS) is oral anticoagulants with an INR intensity between 2-3. This recommendation has been mostly derived from retrospective and prospective randomized studies based on INRs determined at time of thrombosis or the closest available one.  The current recommended anti-thrombotic therapy for patients with anti-phospholipid syndrome (APS) is oral anticoagulants with an INR intensity between 2-3. This recommendation has been mostly derived from retrospective and prospective randomized studies based on INRs determined at time of thrombosis or the closest available one. Objective: To evaluate the rate of re-thrombosis in patients with primary APS (PAPS) during a defined anticoagulation index period.

Methods: We studied patients attending a Tertiary Referral Care Center according to the following inclusion criteria: PAPS (Sydney Criteria), a history of one or more episodes of thrombosis, on oral anticoagulants and ≥2 INR determinations per year. Index period was defined as either the time elapsed between the first available INR and the next thrombotic event or the time between the first and last available INRs in rethrombosis-free patients. We also analyzed the number of thrombotic episodes before the index period. Statistical analysis:  We used X² test, U-Mann Whitney test and Cox survival analysis.

Results: We studied 81 PAPS patients (73% women) with a mean age of 46.8 ± 15.5 years and a median follow-up of 6.4 years (range 0.15-17). Sixty-four patients did not have an episode of re-thrombosis, while 17 had a new episode of thrombosis during follow-up. The latter by definition was longer in thrombotic-free patients (6.7 vs. 1.9 years, p= 0.003). The median INR during the anticoagulation index period was significantly higher in re-thrombosis-free patients (2.5, 1.1-3.6) compared with patients with recurrent thrombosis (1.9, 1-2.9, p=0.001). The median number of INR determinations per years of follow-up was similar in both groups (4.9 vs. 5.7). The number of thrombotic episodes in re-thrombosis-free patients before the index period (1, 1-4) was lower compared with their re-thrombosed counterparts (3, 1-5, p<0.001). Both differences remained statistically different after Cox analysis (median INR: OR 0.13, 95% CI: 0.05-0.32, p<0.001; history of rethrombosis: OR 17.4 (2.2-133.8, p=0.006). No differences were found between the two groups in the frequencies of ant-cardiolipin (IgG or IgM), anti-b₂-glycoprotein-I (IgG or IgM), lupus anticoagulant, triple marker positivity, dyslipidemia, cigarette consumption, aspirin and immunosuppressive therapy, arterial hypertension and diabetes mellitus.

Conclusion: A sustained INR of 2.5 for secondary thromboprophylaxis in patients with PAPS appears to be protective whereas a previous thrombosis confers risk. PAPS patients were more prone to develop recurrent thrombosis if their INR persistently remained beneath that threshold during follow-up.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/sustained-moderate-intensity-levels-of-oral-anticoagulant-therapy-and-the-rate-of-recurrent-thrombosis-in-patients-with-primary-antiphospholipid-syndrome/