NEJM: Warfarin self-testing an option where care is limited

Weekly self-testing to maintain warfarin anticoagulation produced similar results to monthly high-quality clinic testing, suggesting that self-testing could be an option for patients in rural areas or with other transportation challenges, according to the results of the THINRS study published in the Oct. 21 issue of the New England Journal of Medicine.

“Warfarin anticoagulation reduces thromboembolic complications in patients with atrial fibrillation (AF) or mechanical heart valves, but effective management is complex, and the international normalized ratio (INR) is often outside the target range,” the authors wrote. “As compared with venous plasma testing, point-of-care INR measuring devices allow greater testing frequency and patient involvement and may improve clinical outcomes.”

During the THINRS study, David B. Matcher, MD, of the Veterans Affairs (VA) Medical Center and Duke University Medical Center in Durham, N.C., and colleagues randomized 2,922 patients administered warfarin (Coumadin, Bristol-Myers Squibb/Sanofi-Aventis) because of a mechanical heart valve or AF to receive either weekly self-testing at home (1,465 patients) or monthly high-quality testing in a clinic (1,457 patients).

Matcher et al used the time to a first major event of a stroke, major bleeding event or death as the trial's primary endpoint. Eight percent of the study population required caregiver support to perform INR testing, and 98 percent of patients were male and 92 percent were white.

The study followed patients for two to 4.75 years. The researchers found that the differences between the two groups were not significant. The unadjusted hazard ratio for the primary endpoint in the self-testing group was reported to be 0.88. After adjusting for the duration of anticoagulation, the presence or absence of a mechanical heart valve and age, the hazard ratio was 0.90.

The researchers also found no significant differences for stroke, major bleeding episodes or death when comparing the self-testing group to the clinic-testing group, (271 vs. 285, respectively). The results did not differ between the subgroups of patients studied.

The total primary event rate was reported to be 9.2 percent for the clinic-testing group versus 8.1 percent for the self-testing group. More patients in the self-testing group reported to have minor bleeding episodes compared to those patients who were followed-up at the clinic.

Additionally, the researchers found that the percentage of time when the INR was within the therapeutic range was higher in the self-testing group compared to the clinic-testing group and differed by 3.8 percentage points.

At two years, patients in the self-testing group had a greater patient satisfaction with anticoagulation compared to the clinic-testing group, a difference of 2.4 percentage points. Costs were also higher in the self-testing group compared to those in the clinic-testing group, a difference of $1,249.

“Although weekly self-testing did not reduce primary events to the extent suggested by the results of earlier studies, our findings may be useful in considering whether to initiate anticoagulation for a specific patient,” the authors wrote. “Although this result did not translate into substantial reductions in event rates, it may offer some assurance to clinicians who are concerned that with self-testing the INR might not be properly monitored.

“In light of the poor record of usual care and the value of anticoagulation in preventing major events, we recommend that self-testing be considered for patients whose access to high-quality anticoagulation care is limited by disability, geographic distance or other factors, if the alternative would be to withhold a highly effective treatment.”