Predictors of warfarin‐associated adverse events in hospitalized patients: Opportunities to prevent patient harm

BACKGROUND The optimum international normalized ratio (INR) monitoring frequency for hospitalized patients receiving warfarin is unknown. OBJECTIVE Assess relationship between daily versus less frequent INR monitoring and overanticoagulation and warfarin-related adverse events. DESIGN Retrospective cohort study using Medicare Patient Safety Monitoring System data. SETTING Randomly selected acute care hospitals across the United States. PATIENTS Patients hospitalized from 2009 to 2013 for pneumonia, acute cardiac disease, or surgery who received warfarin. INTERVENTIONS None. MEASUREMENTS (1) Association between frequency of INR monitoring and an INR ≥6.0 or warfarin-related adverse event. (2) Association between the rate of change of the INR and a subsequent INR ≥5.0 and ≥6.0. RESULTS Among 8529 patients who received warfarin for ≥3 days, for 1549 (18.2%) the INR was not measured on 2 or more days. These patients had higher propensity-adjusted odds ratios (ORs) of having a warfarin-associated adverse event (OR: 1.48, 95% confidence interval [CI]: 1.02-2.17) for cardiac patients and surgical patients (OR: 1.73, 95% CI: 1.20-2.48), with no significant association for pneumonia patients. Cardiac and pneumonia patients with 1 day or more without an INR measurement had higher propensity-adjusted ORs of having an INR ≥6.0 (OR: 1.61, 95% CI: 1.07-2.41 and OR: 1.92, 95% CI: 1.36-2.71, respectively). A 1-day increase in the INR of ≥0.9 occurred in 621 patients (12.5%) and predicted a subsequent INR of ≥6.0 (positive likelihood ratio of 4.2). CONCLUSION Daily INR measurement and recognition of a rapidly rising INR might decrease the frequency of warfarin-associated adverse events in hospitalized patients. Journal of Hospital Medicine 2016;11:276–282. © 2015 Society of Hospital Medicine