Background/Purpose:  Antiphospholipid Syndrome (APS) is a systemic autoimmune disease characterized by recurrent arterial or venous thrombosis and/or recurrent pregnancy morbidities, with persistently positive antiphospholipid antibodies. Patients with APS who have had a thrombosis require anticoagulation with a vitamin K antagonist (VKA), mainly warfarin, to a target international normalized ratio (INR) indefinitely. The purpose of this study was to investigate whether patients with APS are spending more or less time within therapeutic range (TTR) of INR compared to non-APS controls.

Methods:  All patients within a large, multi-center university hospital system with possible APS who were also prescribed warfarin between July 2012 and July 2015 were first identified, and then chart reviewed for accuracy. True diagnosis was based on an APS diagnosis identified as the reason for anticoagulation in chart notes, or fulfillment of Sapporo criteria for diagnosis of APS while being prescribed warfarin therapy. These patients were then age- and sex-matched with controls, consisting of all non-APS patients who were on warfarin. The TTR for each patient was calculated using the percent of days in range (Roosendaal method). The APS and control patients’ TTR values were compared overall, as well as in subcategories such as the type of thrombotic event, presence of lupus anticoagulant, and enrollment in a pharmacy monitoring program.

Results:  Of 149 patients surveyed, there were 45 APS patients who met all inclusion criteria. These were matched with 45 control patients. There were no differences seen for any of the analyzed variables, including mean INR, when comparing controls with APS patients. As determined by logistic regression analysis, using the 50th percentile as a cut-off, an increase in 10 years of age was associated with having higher TTR [p=0.01, OR=1.91 (1.17-3.12)], though this association was only seen in APS patients, and not in the controls. Positivity for the lupus anticoagulant did not affect TTR. Patients who were enrolled in a pharmacy monitoring program had increased TTR for both controls [p=0.011, OR=5.77 (1.50-22.15)] and APS patients [p=0.011, OR=9.02 (1.64-49.58)]. When comparing TTR values for patients with the same thrombotic event type, most TTR values were similar, however, APS patients with deep vein thrombosis had a higher TTR as compared to the controls (p=0.016).

Conclusion:  APS patients and controls have no significant difference in TTR values, even when analyzing specific manifestations, with the exception of venous thrombosis, which was slightly better managed in APS patients. Young APS patients, but not controls, had markedly decreased TTR, independent of disease duration. Individuals enrolled in a pharmacy monitoring program had, in general, more visits, longer duration of treatment and reached their TTR to a higher degree. Surprisingly, the presence of certain antiphospholipid antibodies also did not impact TTR. This study indicates that there is no evidence that anticoagulation with a VKA (most often warfarin) is particularly difficult, or that TTRs in patients with antiphospholipid syndrome are different in this regard than a control population.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/antiphospholipid-syndrome-patients-time-within-therapeutic-range-of-international-normalized-ratio-inr/