Snail's pace for home INR testing

Content provided by the Faculty of the Harvard Medical School

Snail's pace for home INR testing

FDA-approved machines allow you to test your blood’s clotting potential at home. Why do so few people who take warfarin use them?

Everyone who takes the blood-thinning drug warfarin (Coumadin) — and there are several million of you out there — walks a medication tightrope every day. Take too little warfarin, and you leave yourself open to potentially deadly or disabling blood clots. Take too much, and you’re at risk of developing serious bleeding in the stomach or a hemorrhagic stroke (bleeding in the brain). The right amount, though, offers protection against blood clots with a low risk of bleeding problems.

The trouble is, what’s “right” is often a moving target. Changes in diet, medications, and health affect how the body reacts to warfarin. A blood test called the prothrombin time, which measures how long it takes blood to clot, tells you if you’re in your target range. In a healthy person who isn’t taking warfarin or other anticlotting medicines, the normal prothrombin time is 11 to 13 seconds. Clotting times are usually reported as a standardized comparison against normal, called the international normalized ratio, or INR. If your INR is 2, then it takes your blood twice as long to clot compared with normal blood.

Most people trudge to their doctor’s office or a lab every few weeks to have their INR checked. If you add up transportation time, parking, and waiting for your name to be called, you can spend an hour having this one-minute test. Why not check it at home, like people who have diabetes do with their blood sugar?

Home monitoring isn’t just about convenience. People who check their INRs at home stay close to the recommended target more often than those who go to the doctor’s office for the test. Even more important, people taking warfarin who monitor their INRs at home slash in half their odds of having a heart attack, stroke, deep-vein thrombosis, or other clot-caused problem, according to an analysis of 14 of the best studies of home monitoring, published in February 2006 in Lancet. Home testers are also less likely to have a serious bleeding problem. By one estimate, better control of anticoagulation could prevent half of the strokes related to atrial fibrillation and heart-valve replacement. That translates into about 75,000 fewer strokes a year.

Other studies have shown that people who check their INRs at home feel better about their treatment and are less anxious and stressed by it. Who knows — these side benefits of taking control may be as important to health as getting the INR right!

Some people go a step further. They not only check their INRs at home, but also use the results to regulate their daily dose of warfarin. This can further reduce the possibility of a blood clot or warfarin-related bleeding problem, says Dr. Samuel Z. Goldhaber, an anticoagulation specialist and associate professor of medicine at Harvard Medical School.

Barriers block wider use

The FDA gave the green light to home INR monitors in 1997. These devices, about the size of a calculator, are as accurate as the machines used in large labs. The process is simple. You prick a finger using a sharp lancet that comes with the kit. You squeeze a drop of blood into the small well of a test strip, then slide the strip into the meter. A few minutes later, your INR flashes on the screen.

It’s as easy to do as checking blood sugar, something several million people with diabetes do at home each day. So why are barely 6,000 Americans, of the three million or so who take warfarin, checking their INRs at home?

Right now, Medicare pays for the machine and test strips only for people who take warfarin because they have a mechanical heart valve. That shuts out the two million or so Americans with atrial fibrillation and millions more with deep-vein thrombosis. The rules also define home INR monitors as laboratory tests. So instead of covering the cost of buying the machine and test strips for an individual, as is done for blood sugar monitors, Medicare requires that a doctor or laboratory buy the equipment and loan it to a patient.

If home INR testing was inexpensive, some people and their doctors might bypass Medicare. But the meter costs more than $1,000, and a year’s worth of test strips adds another several hundred dollars.

Some big insurers, spurred by the mounting evidence that home INR testing prevents potentially catastrophic heart attacks and strokes, are already covering the cost of home INR monitoring for people with atrial fibrillation and deep-vein thrombosis.

At some point, Medicare will re-evaluate its home INR testing decision and definition. The mounting pile of evidence, such as that presented in the Lancet paper, will help nudge the test toward more mainstream use.

You can do this

Most people can check their INRs at home. Education isn’t an issue, nor is age. You need some dexterity to do the finger stick, and you must be able to see the machine’s screen and understand the results — or have a partner or friend who can do it for you.

Many doctors don’t know about home INR monitoring. And some who do know about it aren’t comfortable having their patients do this at home, since an out-of-whack INR is more immediately dangerous than an off-target blood sugar.

In other words, if you take warfarin, don’t wait for your doctor to bring up the issue of home INR monitoring. If you think it’s for you, check with your health insurer to see if it covers the equipment, then bring it up with your doctor.

E-mail This | Print This

Last updated:	August 21, 2006