Instability of INRs


Clinical question: Does an initial stable international normalized ratio (INR) predict long-term stability?

Background: Warfarin decreases stroke risk among patients with atrial fibrillation; however, it interacts with food and drugs and requires monitoring to achieve a therapeutic INR. It is unclear if patients on warfarin with an initial stable INR value remain stable over time. Additionally, it is controversial whether patients on warfarin with previously stable INRs should benefit from switching to a non–vitamin K oral anticoagulant.

Study design: Retrospective study.

Setting: Outpatient clinics.

Synopsis: Data were collected from the Outcomes Registry for Better Informed Treatment of Atrial Fibrillation. Included in the study were patients taking warfarin at baseline with three or more INR values in the first 6 months and six or more INR values in the subsequent year. Stability was defined as 80% or more INRs in therapeutic range (2.0-3.0).

Only 26% of patients taking warfarin had a stable INR during the first 6 months, and only 34% continued to have a stable INR in the subsequent year.

Bottom line: Initial stable INR within the first 6 months among patients taking warfarin does not predict long-term INR stability in the subsequent year.

Citation: Pokorney SD, Simon DN, Thomas L, et al. Stability of international normalized ratios in patients taking long-term warfarin therapy. JAMA.2016;316(6):661-663

Dr. Florindez is an assistant professor at the University of Miami Miller School of Medicine and a hospitalist at University of Miami Hospital and Jackson Memorial Hospital.