Hemorrhagic events lead to an increase in international normalized ratio in patients on warfarin

The purpose of this study was to support a theory that in a cohort of patients on warfarin with bleeding and an elevated international normalized ratio (INR), the INR elevation was related to the bleeding episode and not necessarily over anticoagulation from warfarin.

The medical records of patients taking warfarin who presented with a bleeding event and high INR were reviewed over an 18-month period. Data collected included warfarin dose, INR, and hematocrit 90 days before and after the bleeding event. Patients were interviewed to ascertain whether any interactions with warfarin occurred which could explain the high INR.

Eighteen patients were identified who presented with bleeding, a high INR, and no identifiable reason for the elevated INR. A significant increase in INR was observed from baseline to the event (2.5 ± 0.36 vs 6.2 ± 3.19; P = .0002), but the INR during all periods of follow-up did not differ from baseline (P = .35-.99). When compared with baseline, differences in the weekly warfarin dose reached statistical significance when all 12 weeks of follow-up were included (34 ± 13.8 mg vs 32 ± 15.5 mg; P = .01) but were not statistically significant when analyzed 4 to 12 weeks after the bleeding event.

Our observations suggest that bleeding can result in an elevated INR in patients previously stable on warfarin.