For patients who are chronically taking the blood thinner warfarin, weekly home monitoring of the international normalized ratio (INR) is a safe alternative to monthly clinical monitoring, according to new results of The Home INR Study (THINRS; NCT00032591). Although more frequent home monitoring did not improve clinical outcomes compared with regular on-site clinic testing, the safety findings support its use, particularly among patients whose disabilities or geographic distance may limit access to a clinical lab for anticoagulation monitoring.

Warfarin is an effective therapy if it is managed well, which means maximizing the time that is spent at a therapeutic INR (range, 2.0–3.0) or time in the target range (TTR). When the intensity of anticoagulation exceeds the upper INR target, patients are at an increased risk for intracranial and other bleeding; when the anticoagulation intensity is below the INR target, the risk for ischemic stroke rises sharply. Therefore, carefully managed warfarin therapy can optimize the benefit of warfarin for prevention of thromboembolism. In the Anticoagulation and Risk Factors in Atrial Fibrillation (ATRIA) Study, a greater proportion of TTR was associated with a greater net clinical benefit – a composite of the number of thromboembolic events that is prevented by warfarin therapy minus the number of intracranial bleeds that is attributed to anticoagulation [Go AS American Heart Association Scientific Sessions 2007. Abstract 3590].

The goal of the THINRS trial was to assess whether increasing test frequency via home monitoring could further enhance the benefit of warfarin in patients who require chronic anticoagulation. Alan K. Jacobson, MD, Loma Linda University School of Medicine, Loma Linda, CA, presented results from THINRS at the American Heart Association Scientific Sessions meeting in New Orleans.

In THINRS, 2922 anticoagulated patients were randomly assigned to weekly home INR testing or monthly clinical monitoring. Prior to randomization, all patients received training on the home monitoring system and demonstrated proficiency following the testing protocol. All patients were taking warfarin to reduce the risk of thromboembolism that was related to atrial fibrillation or mechanical heart valves.

After a mean follow-up of 3 years, 7.9% of patients in the home monitoring group and 8.9% of those who were undergoing clinical testing reached the primary composite endpoint of ischemic stroke, major bleeding, or death. Although time to first major event trended in favor of home monitoring, the benefit was not statistically significant (HR, 0.87; 95% CI, 0.73 to 1.03; p=0.10).

According to an analysis of secondary endpoints, home monitoring modestly improved the total TTR compared with clinic monitoring (70% vs 62%). Home INR monitoring also improved patient satisfaction with anticoagulation treatment, as measured by the Duke Anticoagulation Satisfaction Score (47 vs 49).

Alan S. Go, MD, Kaiser Permanente of Northern California and University of California, San Francisco, CA, questioned whether THINRS was underpowered to demonstrate a reduction in the most relevant outcomes of ischemic stroke and intracranial bleeding with home monitoring compared with clinic INR testing but noted that the absolute number of ischemic strokes or intracranial bleeds was essentially the same in both treatment arms. Due to effective anticoagulation – as shown by a cumulative TTR of >62% in both study arms – patients had very low event rates. THINRS reinforces the importance that high-quality anticoagulation, regardless of the method of monitoring, leads to low rates of ischemic stroke and intracranial bleeding, he said.

“Home INR monitoring with coordinated follow-up is a reasonable alternative for appropriate patients with mechanical valves, atrial fibrillation, and venous thromboembolism,” Dr. Go concluded. Additional secondary outcomes from THINRS, including other clinical events, compliance with self-testing, quality of life, and cost-effectiveness, will be reported in future presentations.