Daily INR Measurement for Inpatients Could Improve Safety

More frequent international normalized ratio (INR) monitoring of hospitalized patients taking the anticoagulant warfarin could increase patient safety, according to a study published online Dec. 14, 2015 in the Journal of Hospital Medicine. Specifically, the authors say, daily INR measurement and recognition of a rapidly rising INR could decrease the frequency of warfarin-associated adverse events.

Warfarin is one of the most common causes of adverse drug events, yet there is limited evidence to guide appropriate warfarin monitoring frequency for hospitalized patients. In 2015, the Joint Commission (JC) reissued its anticoagulant-focused National Patient Safety Goal, which mandates the assessment of baseline coagulation status before starting warfarin, and calls for warfarin dosing based on a "current" INR, although current is not defined. In the present study, the researchers retrospectively analyzed Medicare Patient Safety Monitoring System data to identify patients hospitalized from 2009 to 2013 for pneumonia, acute cardiac disease (myocardial infarction or heart failure), or surgery, who received warfarin. If a patient's INR level never reached above 1.5, they were excluded from analysis.

The researchers identified 14,217 patients, of whom 1,055 (7.4 percent) developed a warfarin-associated adverse event. Warfarin treatment was started on the first day of hospitalization for 6,825 patients (48.0 percent). Among these patients, the vast majority (95.8 percent) had an INR measured within one day. The authors say this showed a high level of adherence to this JC safety standard.

However, among the 8,529 patients who received warfarin for three or more days, INR was not measured on two or more days for 18.2 percent of patients. Patients who had two or more days on which the INR was not measured had higher rates of INR at 6.0 or above, compared to patients for whom the INR was measured daily. Overall, patients with no INR measurement for two or more days had 48 percent higher chance of having a warfarin-associated adverse event, compared to patients with daily INR measurement. The odds were even higher (73 percent) for cardiac and surgical patients, but with no odds difference for pneumonia patients. Furthermore, a 1-day increase in the INR of 0.9 or higher occurred in 12.5 percent of patients and predicted a subsequent INR of more than 6.0.

"Because our results suggest that lapses in INR measurement lead to over-anticoagulation and warfarin- related adverse events, it may be appropriate to measure INRs daily in most hospitalized patients receiving warfarin," write the authors led by Mark Metersky, M.D., from University of Connecticut in Farmington. "Our results suggest that use of a warfarin dosing protocol that considers both the absolute value of the INR and the rate of rise could reduce warfarin-related adverse events. … These results provide actionable opportunities to improve safety in some hospitalized patients receiving warfarin."