Patient Education Blog

INR Self-Testing

Stephan Moll, MD writes…

Patients on warfarin need their blood levels monitored through a blood test called INR (International Normalized Ratio). Classically, this is done through a physician’s office or an anticoagulation clinic.  Testing can be done through an i.v. blood draw, with blood then being sent off to a lab for INR testing. Or it can be done through a finger-stick and testing on a so-called POC device (or point-of-care device) in the office, with results being immediately available. POC devices give reliable INR results.

INR Home Testing is Reliable, Safe and Effective

INR point-of-care devices are also available to patients for INR home testing. They are often reimbursable by insurance carriers.  And warfarin management through patient self-testing at home is at least as effective and safe as INR testing through a medical practice. The well-done large 2011 THINRS trial clearly showed this, and a recent systematic review of the medical literature confirms that [ref 1,2].

If I were a Patient on Warfarin…

If I were a patient on long-term warfarin, I would want an INR home monitor.  It would give me independence; wouldn’t have to waste my time with clinic visits just to have my INRs checked; have breakfast – stick finger, get INR– go to work or play. That’s what I’d want, short of preferring to be on a well-established, reversible oral anticoagulant that does not require routine anticoagulation monitoring.

Why Is INR Self Testing Not More Popular in the U.S.?

All published data convince me that INR home testing is effective and safe and the right thing to do – in appropriately selected and well-trained patients. Of course, some patients are not suitable for self-testing. But the THINRS trial showed that a great many patients (80 %) are suitable and trainable. So why do many physicians and anticoagulation clinics not offer it to their patients?

  1. Reimbursement reasons: Yes, the testing devices and test strips are often paid for by insurers, but INR home testing is unattractive for many health care practice settings because of the often un-billable phone management services or the loss of income from not having patients come to billable clinic visits. Yes, one can bill for the phone management service, but the reimbursement (ca. $10.00 per month) is often not worth the effort needed to collect that money. There is, regrettable, not much financial incentive to offer INR home testing to patients.
  2. Hassle: Getting a patient a device, getting the patient’s INR results phoned into the clinic, and managing warfarin over the distance is involved with some hassle, paperwork, a need for a good clerical structure to make this a safe management option. Many health care providers seem to perceive the hassle of this not worth the effort.
  3. Control: A number of health care providers are hesitant to give up control and may feel vulnerable to litigation if a bad outcome (bleed or thrombosis) happens to their patient who does INR home monitoring. The present systematic review should aid in dispersing that concern, as it shows that outcomes in appropriately trained patients are not worse than in individuals who receive anticoagulation monitoring care by coming to a clinic for INR testing. I have actually heard the provocative comment that physicians who do NOT offer their patients INR home testing are liable if a bad outcome occurs, as the present systematic review showed that INR home monitoring is associated less thrombotic events and should, thus, be the preferred management strategy. I wouldn’t go so far to support that statement, but it reflects that one could certainly present INR home testing in suitable patients as THE gold-standard of care.
  4. Lack of awareness and knowledge:  There may also be a component of unawareness – amongst health care professionals, and clearly amongst patients on warfarin – that INR home testing is available, reliable, safe and effective. Hopefully, the THINRs trial and the present systematic review help increase awareness of this viable monitoring option; and disperse the unwarranted concerns that INR home testing devices are not reliable or the majority of patients not suitable for it.


I conclude as I started: If I were a patient on long-term warfarin, I would want an INR home monitor. I am afraid, though, my physician or anticoagulation pharmacist would say: ‘Can’t do it; our practice is not set up to do it; too much hassle, too much paperwork, no worthwhile reimbursement’. I bet if I were to beg enough, they would eventually provide me with the INR home monitoring option – but only as a favor to me as a medical colleague and as an exception to their practice. I wish, however, that every suitable patient could have the option of having warfarin managed via INR home monitoring. It is safe and effective and the right thing to do for good patient service. My advice to patients interested in INR self-testing: tell the pharmacist and MD who manages your anticoagulation that you are interested in INR self testing and ask them whether they would support it.


  1. Matchar B, Jacobson DB, Dolor R et al. Effect of home testing of international normalized ratio on clinical events. N Engl J Med, 2010; 363: 1608-1620.
  2. Heneghan C et al. Self-monitoring of oral anticoagulation: systematic review and meta-analysis of individual patient data. Lancet. Available online 30 November 2011.


Disclosure:  I have received research support (material support, not financial) from International Technidyne Corporation.


Last updated: Jan 25th, 2012

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5 Responses to “INR Self-Testing”

  1. APSFA says:

    It is worthwhile to mention that finger stick machines are not accurate for some patients, e.g. patients with Antiphophospholipid Antibody Syndrome.

    • Mike says:

      As someone with a strong case of APS, I found myself to be one of the 1/3rd of APS patients who consistantly tests high when using a hand held. In my case a INR 3.5 vein stick would test 5.5 on my hand held. Problem? Nope. I created an Excel spreadsheet and log my hand held results…as long as my hand held reports INR 4.5-6.5 I am usually within my vein stick INR 3.0-4.0 theraputic range. At least once a year I visit my GP and/or Hemo…I always have them perform the PTT via vein stick, and with in few minutes I poke myself and test on my hand held. I log both and generally always find similar results. Heck last time my GP called and said I had a 8.1 INR…I did two consecutive strips myself with 4.6 & 4.7 results…had a 2nd vein stick and determind the lab had fat-fingered my initial results…my actual was 3.1 not 8.1

  2. Laura says:

    My clinic would probably get on board with self-testing, but my hematologist nixed the idea due to having had a bad experience with another patient who self-tested a few years ago. So if patients aren’t compliant early on, it kinda ruins it for people down the line. I’ll revisit the idea periodically with my primary – maybe someday I’ll get a yes!

  3. Michele Walker says:

    I have been home testing for two months and like it much better than going to the clinic every six weeks. However, the negative I’ve experienced is that now it seems as though my INR isn’t as stable. For two years I was within therapeutic range with the exception on twice and one of those was because of getting back to my range after bridging to have a throat biopsy. Since being on the home monitoring, I am constantly having to adjust my RX and re-check. One of the reasons I didn’t mind being on Warfarin long-term was the fact that they weren’t constantly having to adjust my dosage. Now, however, I am starting to question whether or not I want to deal with it. Is it common to have more flucuations in home testing?

    • Stephan Moll says:

      No, it should not be more common to have INR fluctuations with INR home testing. I wonder, though, as you are new to INR home testing, whether it is a matter of gaining more eperience, so that the fingersticks and getting the blood are more consistent. Review your technique with somebody knowledgeable.