Warfarin Home Testing a Viable Alternative to Lab Testing

Researchers at Lenox Hill Hospital (New York, NY, USA) conducted a retrospective analysis of the Self-Testing Analysis Based on Long-Term Experience (STABLE) study, evaluating more than 29,500 warfarin patient self-testers (PST) for more than two years. Three-quarters of the patients were on warfarin for nonvalvular atrial fibrillation (AF), while the others suffered from valvular disease alone or combined with AF and venous thromboembolism.

The results showed that the rate of TTR for those who self-tested was 69.7% for all self-testers and 74% for those who tested weekly. Compared with younger patients (46-64 years), older patients (65-74 years) had higher a rate of time in target range (67% versus 72%); men had a slight edge in percent TTR (72%) over women (66%). The PSTs also benefited from major reductions in the number of critical-value international normalized ratio (INR) results, which can triple the risk of a major bleeding event or stroke. The study was presented at the American College of Cardiology (ACC) annual scientific session, held during March 2012 in Chicago (IL, USA).

“The STABLE study dispels many myths surrounding safe warfarin treatment, particularly those related to the drug’s use in the elderly population and that population’s ability to successfully self-test,” said lead author and study presenter anticoagulation expert Jack Ansell, MD. “Home monitoring achieves better outcomes because it's convenient for patients, the test is consistent, and the immediate awareness of test results empowers patients and enhances compliance.”

Warfarin is an anticoagulant initially introduced in 1948 as a pesticide against rats and mice and is still used for this purpose. In the early 1950s warfarin was found to be effective and relatively safe for preventing thrombosis and embolism in many disorders. Despite its effectiveness, treatment with warfarin has several shortcomings. Many commonly used medications interact with warfarin, as do some foods, and its activity has to be monitored by blood testing for INR to ensure an adequate yet safe dose is taken. A high INR (more than 5) predisposes to a high risk of bleeding, while an INR below the therapeutic target (less than 1.5) indicates that the dose of warfarin is insufficient to protect against thromboembolic events.

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