Home Monitoring for Warfarin Therapy

Home Monitoring for Warfarin Therapy

The Status of INR Home Monitoring for Warfarin Therapy

Warfarin has been the principal oral anticoagulant (blood thinner) in use in the United States for a variety of blood clotting (thrombotic) diseases since the 1950s. Warfarin therapy, however, has many drawbacks, principally among them, the complexity and labor intensiveness of managing therapy and the high risk of adverse events often due to poor dose management. Anticoagulation clinics, focusing predominantly on managing warfarin dosing, are now commonplace, and generally result in better outcomes than individual physicians managing a small group of patients (denoted as “usual care” to differentiate it from anticoagulation clinic care).

In the late 1980s, a new technology for monitoring the prothrombin time (PT) or INR (International Normalized Ratio) was introduced employing small portable instruments that made it possible for patients to perform an INR from a finger stick sample of blood, much as blood sugar is measured in diabetics.

These point-of-care (POC) instruments are now widely used in physician offices. Given their size, portability, and ease of use, these devices also allow patients to measure their own INR at home, which we call patient-self testing (PST), and with proper education, manage their own anticoagulation dosing (patient-self management or PSM). Exhaustive correlation studies have been done to assess the accuracy and precision of POC instruments with INRs drawn from an arm vein. When tested under controlled conditions, POC devices have consistently confirmed the adequacy of this methodology for the monitoring of oral anticoagulation.

Home INR Monitoring

There was great hope that developing home monitoring models of care would vastly improve the outcomes of therapy and this hope has proven true. A number of clinical trials demonstrated improved quality of care as reflected by patients being in therapeutic

INR range a greater percentage of time, as well as a reduction in major complications such as major bleeding or thrombosis when compared to other models of care. However, the hope-for-widespread application of such testing did not develop in the United States until recently. Currently, more than 100,000 individuals are monitoring their own therapy at home.

What are the benefits of home monitoring?

Home monitoring provides four major benefits. These include:

  1. Convenience for the patient;
  2. The ability to monitor an INR frequently;
  3. Consistency of testing reagents and instrument
  4. Patient empowerment by involvement in their own care. It is particularly beneficial for those individuals who travel and monitor their INR while away from home.

Who is eligible for home monitoring?

In general, patients must be willing, able, and compliant with monitoring. Thus, a patient should show good compliance with previous anticoagulation management; have the manual and visual dexterity to perform self testing or else have a care provider at home who can perform the test; and have a physician that supports home monitoring.

What are the barriers to home monitoring?

A number of factors have served as barriers to implementation of home monitoring in the US. The lack of physician education of the benefits of this technology has been a barrier. Questions about the safety and accuracy, as well as physician liability have also been a barrier. Finally, the long delay in Medicare approval for reimbursement for the cost of the instrument, for implementation of home monitoring, and for physician management has been an important barrier. Recently, Medicare expanded its reimbursement policy to include patients who are anticoagulated for mechanical heart valves, atrial fibrillation, and venous thrombosis. Home monitoring is now largely implemented through companies called independent diagnostic testing facilities (IDTFs). These businesses will provide instruments, train patients, and often keep track of the

INRs for physicians who prescribe home monitoring. Reimbursement is provided on a per test basis after the initial reimbursement for training and implementation.

The problem of reimbursement for home monitoring is not unique to the US, but is a problem throughout the world. Because of this, patient advocacy groups have sprung up in a number of countries to lobby their respective health care systems to cover such services, and many of these groups have been successful (see: www.ismaap.org to learn more about these international advocacy groups). In the US, no specific groups currently exist, but the National Blood Clot Alliance, a patient advocacy group for individuals with blood clotting problems does promote this model of anticoagulant care.


For now, most anticoagulation therapy in the US is still managed by the individual physician. While anticoagulation clinics, managing large panels of patients, continue to grow at a rapid rate, the growth of patient home monitoring is also expanding significantly. For those of us who understand the benefits of PST/PSM and who are committed to improving patient care, we will continue to educate and advocate for our patients with the long-term objective of providing the best possible model of anticoagulation care available.

Jack Ansell, MD

Jack Ansell, MD, MACP is the Former Chair of the Medical and Scientific Advisory Board of the National Blood Clot Alliance.

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