Self monitoring does not improve warfarin clinical outcomes
MedWire News: Allowing warfarin users to self-test their international normalized ratio (INR) every week at home results in a small increase in the time spent within a therapeutic range relative to monthly clinic testing, but does not delay the onset of major clinical events, show the results of THINRS.
All of the 2922 patients in THINRS (The Home INR Study) were trained to competence with point-of-care INR devices. They were randomly assigned to use these devices for weekly self-monitoring of their INRs or to attend for monthly high-quality clinic testing.
During follow-up lasting between 2.00 and 4.75 years, patients in the self-testing group spent 66.2% of their time within a therapeutic INR range, compared with 62.4% in the clinic-testing group. This 3.8% difference was statistically significant.
Despite this, the primary endpoint of time to the first major clinical event (stroke, major bleeding, or death) did not differ between the two groups, David Matchar (Duke University Medical Center, Durham, North Carolina, USA) and colleagues report in the New England Journal of Medicine.
Major bleeding was the most common primary endpoint event, occurring at annual rates of 4.0% and 4.7% in the self-testing and clinic-testing groups, respectively. Stroke occurred in 0.7% of each group annually.
Patients in the self-testing group reported more minor bleeding events, at 540 versus 401 for the clinic-testing group, but the team believes that "this may be due to the more frequent contact with the THINRS study staff in this group as compared with the clinic-testing group."
Patients who self tested were significantly more satisfied with their anticoagulation therapy than were those assigned to clinic testing, and they reported a higher general quality of life.
Matchar et al note that although self testing did not have a large positive effect on clinical outcomes, the study results do not rule out a small positive effect and definitely rule out any negative effect.
"In the 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," they conclude.
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By Eleanor McDermid