Beware Falsely Elevated INRs
Elevated international normalized ratios (INRs)—which are linked to bleeding complications—are rare, but they may be falsely elevated if patients are undergoing hemodialysis.
A recent cross-sectional study at Kaiser Permanente followed nearly 30,000 adults receiving anticoagulants. From January 2000 through December 2004, the patients were monitored by a centralized anticoagulation service, which calculated the prevalence of all elevated (a value of 10 or higher), falsely elevated, and truly elevated INRs.
Of the 556,990 INRs included in the analysis, 793, 53, and 740 INRs were elevated, falsely elevated, and truly elevated, respectively, according to a report in Chest (2007;131:816-822). Being on dialysis at the time of the elevated INR measurement increased the likelihood of a falsely elevated measurement nearly 10 times, making this the strongest independent predictor of a falsely-elevated INR.
A low target INR was the only other factor found to be an independent predictor of a falsely elevated INR. Conversely, patients with a truly elevated INR were more likely to reside in a nursing home and have been prescribed anti-infective agents.
Patients presenting with elevated INRs are a significant challenge. Patients with high INRs and evidence of significant bleeding should be treated aggressively with vitamin K and exogenous clotting factors, the researchers noted.
For asymptomatic patients, they caution, clinicians should consider the possibility of false INR elevation as part of the therapeutic plan. “Confirming the accuracy of the elevated INR result,” they conclude, “may prevent the inappropriate reversal of anticoagulation therapy, and the attendant potential for thrombotic complications or refractoriness to continued warfarin therapy.”