Warfarin Works with Either At-Home or Clinic Testing

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WASHINGTON, DC—Patients taking warfarin, a widely used blood-thinning pill that requires careful dose monitoring, have similar outcomes whether they come to a clinic or use a self-testing device at home, according to a recent VA study.  The findings, published in the October 21 issue of the New England Journal of Medicine, are good news for heart patients who live far from clinics or are homebound.

“This study helps answer an important question for cardiologists, primary care physicians, and other health providers, and will lead to improved care for their patients,” explained VA research chief and cardiologist Joel Kupersmith, MD. “The results are significant for a great number of veterans currently receiving care through VA.”

Traditionally, doctors, pharmacists, and nurses monitor patients who are taking warfarin, sold as Coumadin®, over several clinic visits. They test how fast the blood clots and adjust the dose accordingly. Doses that are too low will not prevent dangerous blood clots, and blood flow to the heart, brain, or other areas of the body could be inadvertently blocked. Doses that are too high could lead to dangerous internal bleeding. 

Patients have the option of tracking their own blood response at home, using blood analyzers known as international normalized ratio (INR) monitors. Patients do a finger stick, apply a small amount of blood to a test strip and feed the strip into the device.  The procedure resembles the one used by people with diabetes to check their blood sugar.  Patients can then call in the results to their provider and get advice on dose adjustments without coming to the clinic. In some cases, they can even set the proper dose of warfarin on their own.   

The authors of the VA study expected home monitoring to work better than clinic monitoring, partly because self-testing can be done at home more frequently—weekly, compared with the typical monthly schedule of the best clinic-based monitoring.  As a result, off-target INR values can be adjusted more regularly and more quickly.  

However, the VA study found little difference between weekly self-testing and monthly testing by clinic-based care teams in the measured outcomes, which are strokes, major bleeding incidents, and death.

The study did find, though, that self-testing at home may offer advantages in other areas. It moderately boosted patients’ satisfaction with the medication and slightly increased the length of time they were in the appropriate dose range.  Researchers said the main message of the study is that patients who are systematically monitored—regardless of the means—are likely to have good outcomes.

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