A study in the Journal of Thrombosis and Haemostasis was able to demonstrate that patients who were successfully managing their warfarin therapy could safely go beyond a month’s time between International Normalized Ratio (INR) blood draws. INR draws typically take place every 4 weeks to monitor patients on blood thinners. “We wanted to see if we could reduce the burden of frequent INR blood tests for patients who are very stable in managing their warfarin,” Geoffrey Barnes, MD, first author of the research and a cardiologist at the University of Michigan’s Frankel Cardiovascular Center, told CLN Stat.Fewer blood draws also means that nurses in the anticoagulation clinic would have fewer INR lab results that they had to process and manage, Barnes said.

The American College of Chest Physicians in 2011 had issued a recommendation favoring INR testing every 12 weeks in stable warfarin patients, following the results of a single center trial that indicated the approach was safe and feasible. Despite these promising results, the approach had yet to be adopted in the clinic setting.

Barnes’ study, the Michigan Anticoagulation Quality Improvement Initiative tested this approach on a broader scale, enlisting six anticoagulation centers in 2014 to extend their standard 4-week protocol for stable warfarin patients. All six did so, establishing a maximum of either 6 or 8 weeks. Among more than 3,360 warfarin-treated patients managed by these centers, 890 patients qualified for extended INR testing, 86.5% of which had their testing interval extended at least once. Through this method, the percentage of patients waiting longer than 5 weeks between blood draws increased from 41.8% in 2014 to 69.3% in 2016.

“Eligible patients who had at least one extended INR testing interval had no significant differences in warfarin anticoagulation indications, gender or bleeding risk from patients who never had an extended INR testing interval despite being eligible,” the researchers indicated.

The study demonstrated that anticoagulation clinics can successfully identify stable warfarin patients and recommend less frequent INR testing. It also showed that the approach was safe, without any increased risk of bleeding or emergency department visits. “Although this data had previously been tested in a randomized trial, our study demonstrates that this strategy can be implemented in a wide variety of anticoagulation clinics,” Barnes said. In following up with these patients, his team found that many of their centers were getting more comfortable with longer time periods between INR blood draws.

“We will continue to study these patients to assess the safety and efficacy of this approach,” he said.