Patient Education Blog

Warfarin therapy made easier

Background and Summary

Patients on warfarin can test their own INR (International Normalized Ratio) at home with small, handheld INR monitors, similar to diabetics checking their own blood sugar. A very large, well conducted study published on Oct 21, 2010 in the New England Journal of Medicine (ref 1) shows that patients can safely and effectively monitor their warfarin therapy themselves with INR home monitors. While this does not come as a surprise to many, this is the first very large and well designed trial to show this.

The study

  • The study enrolled 2,922 patients with irregular heart beat (atrial fibrillation = a. fib) or mechanical heart valves on warfarin therapy. Approximately half of the patients were randomly assigned to be followed in a structured anticoagulation clinic (= warfarin clinic) with once monthly INR testing. The other half received an INR home monitor to measure their own INR weekly, with results reported back to their health care professional for warfarin dose adjustments.
  • Both patient groups did equally well – they had the same risk of major bleeding and stroke. In addition, both groups had similarly well controlled INRs, even though they were slightly more often in the desired (=therapeutic) range in the self-testing group. In addition, the self-testing patients were slightly more satisfied with anticoagulation therapy and had slightly better quality of life.
  • Noteworthy is also, that of all patients evaluated for the study, the majority (80 %) were able to reliably use the INR home monitor – either on their own or with the aide of a care provider. This is contrary to the often heard comment from physicians that “my patient is not suitable for INR home testing”. The study shows that many patients on warfarin are capable of safe INR home testing.



These INR devices (Coaguchek, INRatio, ProTime) have been available for many years and are in wide use in many European countries. However, in the U.S. their use has not taken off. This has been disappointing, as they are reliable and had previously also been shown in smaller studies to be safe and effective (ref 2). At first, this lack of uptake was due to the fact that insurance carriers did not pay for these devices and the INR test strips. However, this has become less of a hurdle since CMS (Centers for Medicare and Medicaid Services) approved Medicare reimbursement for these instruments in 2008. However, as of 2010, health care professionals are – understandably – often not willing to prescribe these instruments to their patients, as the health care provider is left with having to make phone calls about INR results and warfarin dose adjustments, without getting appropriate reimbursement for these services. This is unfortunate.

For me it is clear: If I was on warfarin, I would want an INR home monitor. It would give me independence: I could time-efficiently test my INR whenever needed, without the need to spend time going to a physician’s office.

My advice to patients: If you are on warfarin, talk to the professional health care provider who monitors your warfarin and ask him/her whether he/she would support you getting an INR home monitor.


1.     Matchar D et al. Effect of home testing for International Normalized Ratio on Clinical Events. N Engl J Med 2010;Oct 2;363:1608-1620.

2.     Heneghan C et al. Self-monitoring of oral anticoagulation: a systematic review and meta-analysis. Lancet 2006;367:404-411.

Disclosure:  I have received  support for a research study investigating the performance of point of care INR monitors in patients with antiphospholipid antibodies from Roche Diagnostics, International Technidyne Corporation (ITC), and Hemosense. I have consulted for ITC.

Last updated: Nov 20th, 2010

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