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At-home warfarin self-monitoring effective for INR control
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At-home patient self-monitoring of warfarin therapy yielded similar results to monitoring performed in a clinic setting and randomized trials, particularly among those who self-tested on a weekly basis, according to findings from the STABLE study.
In a retrospective cohort study, researchers collected data on 29,457 patients from the database of an independent diagnostic facility (Alere Inc.), including anticoagulation data and documentation of at-home patient self-monitoring of international normalized ratio (INR) range. The researchers queried the database for information on all warfarin recipients trained to perform self-monitoring on or after Jan. 1, 2008, who had completed at least 6 months of patient self-testing before June 30, 2011.
The study included two cohorts for analysis: variable/nonweekly testers (those who tested every 2 to 4 weeks, n= 24,907) and weekly testers (n=4,550). Across both groups, the mean age was 70.5 years upon initiation of self-testing, and 56% of participants were male. Mean patient follow-up duration was 17.2 months in the weekly testing group and 14.5 months in the variable tester group.
The primary surrogate endpoint was time in the therapeutic INR range (TTR), as measured by the Rosendaal method. The secondary surrogate endpoint was critical INR values (INR <1.5 or INR >5) in each group. Four patient characteristics also were assessed: age, primary warfarin indication, sex and self-testing duration.
The mean TTR for the entire population was 69.7%, with a higher TTR among the weekly testers (74% vs. 68.9% in the variable testing group; P<.0001). Mean TTR was significantly higher among weekly tests vs. variable/nonweekly testers regardless of demographics or other evaluated patient characteristics. Older patients had a higher TTR than younger patients (71.5% for those aged 65-74 years vs. 67% among those aged 46-64 years).
Critical INR values occurred in 49.8% of all patients. Patients with low mean TTR were at significantly increased risk of experiencing a critical INR value (HR=3.16; 95% CI, 1.89-2.22). Researchers noted that variable/nonweekly testers were more likely than weekly testers to have low TTR (29.8% of patients vs. 17.1%; OR=2.05; 95% CI, 1.89-2.22); however, adjustment for test frequency weakened this association (HR=1.15; 95% CI, 1.12-1.17 for weekly vs. variable frequency).
“This retrospective analysis offers the first insights into surrogate outcomes for patients on warfarin who were managed via home [patient self-testing] with the support of a health management service in a real-world setting,” the researchers wrote. “… The analysis confirmed that in the United States, a wide variety of patients successfully perform [self-testing] and sustain high surrogate endpoints of high TTR with low incidence of critical INR values over time.”
Disclosure: Several researchers reported employment with Alere Inc., which funded the study. One researcher also reported serving as a paid consultant for the company.
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