Warfarin Monitoring in Antiphospholipid Syndrome and Lupus Anticoagulant

Abstract

Objective: To review the available literature on international normalized ratio (INR) and chromogenic factor X (CFX) monitoring in patients with antiphospholipid syndrome (APS), specifically lupus anticoagulant (LA), and furthermore, to identify benefits of one monitoring test compared with the other in the presence of LA. Data Sources: A literature search was conducted through MEDLINE (1946-May 2014) utilizing the following MeSH terms chromogenic compounds, anticoagulants, and factor X. Further articles were identified from original literature citations. Study Selection: All English-language studies were included that involved INR and/or CFX monitoring in APS patients that focused on a therapeutic anticoagulation level with warfarin therapy. Data Synthesis: A total of 55 articles were identified, of which nine are referenced because of their relevance for this review: three articles focus on the efficacy of utilizing INR monitoring in patients with APS, five focus on CFX compared with INR for therapeutic warfarin dosing, and one compares different thromboplastins utilizing both INR and CFX monitoring. INR monitoring in patients with APS, specifically LA, was not found to be reliable because thromboplastin reagents are sensitive to LA. Furthermore, when INR was compared to CFX, patients with LA had supratherapeutic INRs despite having CFX within goal range. Conclusions: In a subgroup of APS patients, INR monitoring may not be safe for determining the dose of warfarin because their INR values can be falsely elevated. Although CFX monitoring is more accurate, it too comes with its own downsides. Managing warfarin therapy in the APS population needs to be individualized.