Anticoagulation quality in antiphospholipid syndrome according to INR testing strategy

Uncertainty exists regarding the accuracy and clinical utility of point-of-care (POC) International Normalized Ratio (INR) testing in patients with antiphospholipid syndrome (APS) prescribed warfarin.

The objective of this study was to evaluate anticoagulation quality among APS patients using different INR testing methods. This retrospective observational cohort included adult patients on warfarin with ≥8 months of INR data and investigator-confirmed APS classification. Patients were categorized by INR testing methods during the 13-month period as POC, venipuncture (VP), or mixed if neither POC nor VP methods accounted for ≥75% of INRs. Outcomes included time in therapeutic range (TTR) and clinical adverse events during the study period.

A total of 93 patients were included (POC n = 49, VP n = 27, and mixed n = 17). The TTR in the overall non-APS clinic population was 63.1% compared to 62.7% in all APS patients. Mean TTR was similar between POC (64.8%) and VP (64.9%) groups, and numerically lower in the mixed group (53.2%), p = 0.18. Patients with arterial thrombosis, triple positivity, or lupus anticoagulant had statistically significantly poorer TTR using the mixed method compared to POC or VP methods. Two thromboembolic events (2.2%) occurred, both in the POC group; and 10 clinically relevant bleeding events occurred (10.8%), distributed among groups.

POC INR testing method demonstrated similar anticoagulation control compared to VP testing among APS patients; however, mixed testing strategies were associated with poorer INR control, especially in patients with arterial thrombosis, lupus anticoagulant, and triple positivity. Further study is needed to explore patient characteristics that predict stability with the POC vs VP method.