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Portable devices make home blood INR monitoring as easy as ABC

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Monitoring the time it takes for blood to clot is a normal but often cumbersome part of healthcare for people taking oral anticoagulation (blood thinning) medication. Doctors adjust the amount of anticoagulants a person takes based on their test results, with the aim of achieving blood that is not too thick and not too thin, but just right.

In Australia blood tests are usually performed in laboratories, meaning that people testing their blood needed to visit a doctor, have a blood sample taken, wait for their results, and speak with their doctor about any consequent dose adjustment that may be required.

Blood monitoring devices which give instant results are becoming increasingly popular, and have the potential to make blood monitoring in the home or health facility as easy as ABC.

Professor Alexander Gallus, Director of Pathology at Flinders University, said, “Testing INR with portable devices enable quick access to results that can be delivered to the patient face to face. This makes it possible for the doctor to ask any essential questions and adjust the dose as necessary on the spot.”

Dr Jackson, of the University of Tasmania School of Pharmacy, said that portable device monitoring “has the potential to change the lives of about 25,000–50,000 patients taking warfarin every year (there are about 250,000 patients on warfarin at any one time in this country).”

INR monitoring made easy

Portable monitoring devices measure the international normalised ratio (INR), which is a standard measure of the blood’s clotting time. Typically, the INR is monitored at least monthly in people taking oral anticoagulation therapy to thin their blood and prevent complications such as stroke or bleeding. Various complications may occur if the blood is too thick or too thin.

Portable devices measure blood clotting time using a drop of blood from the fingertip. The blood is placed on a test strip which is inserted into the device. The time the blood takes to form a clot is measured and converted to an INR result displayed on the device’s screen in about 30 seconds.

Using a portable device to monitor blood clotting time takes just a couple of minutes, meaning no waiting for test results as is the case with laboratory testing. Independent self-monitoring with a portable device can be performed at home, meaning that people requiring the tests don’t need to waste time and money travelling to health centres. Even those people who are unable to self-monitor can have their blood checked at a healthcare facility (e.g. their GP’s clinic) with a portable device and get immediate results and dose adjustments.

Not too thick, not too thin, just right

Portable devices make blood INR monitoring easier and make more regular monitoring feasible. More regular monitoring enables more regular dose adjustments. This has been shown to increase the amount of time blood thickness is in the ‘therapeutic window’, when the blood thickness is just right.

Dr Jackson said that, “unfortunately, there is a very narrow therapeutic range for warfarin,” and regular INR testing can identify when the INR is too high or too low.

“Dose changes can then be made to ensure that the INR is within the target range.”

When blood INR is monitored monthly, a person taking oral anticoagulants can expect to keep their blood thickness ‘just right’ about half the time. With weekly monitoring and dose adjustment, a ‘just right’ blood thickness can be achieved 85% of the time.

Maintaining the right blood thickness reduces the risk of life-threatening complications. Normally, blood only clots when a person starts to bleed, but in some people blood clots form in the blood vessels when there is no active bleeding. The clots may circulate in the blood, and if this happens, a clot may get stuck in a blood vessel and prevent blood from flowing to the body’s organs. A clot that gets stuck in the brain can cause a stroke, while one that gets stuck in the heart can cause a heart attack.

The principle behind oral anticoagulation therapy is to keep the blood sufficiently thin to prevent the formation of clots. However, it is important to make sure the blood does not become too thin, as very thin blood is also dangerous. When the blood is too thin it is unable to form clots, which means that a person who starts bleeding does not stop. Uncontrollable bleeding can lead to major blood loss, which can be just as life-threatening as a stroke or heart attack.

Balancing act

Determining the correct dose of oral anticoagulants is a balancing act between making the blood too thin and risking bleeding, and making the blood too thick and risking blood clots. It can be a very difficult act for doctors to perform.

Oral anticoagulants affect different people differently; the same dose of medication can cause different blood clotting times in different people, so a doctor cannot simply prescribe one person the same dose as another and hope to achieve the correct blood thickness. To complicate things further, the effect of blood-thinning medications on an individual can also change from day to day.

For example, Dr Jackson said, “Diet, alcohol, illness, other medications can all affect the response to warfarin.”

Easier blood testing equals more regular monitoring

The only way of determining the effect of a blood-thinning medication for an individual person at a particular time is to monitor blood clotting time. The more regularly blood monitoring is performed, the more often dose adjustments can be performed to maintain a desirable blood thickness.

However, laboratory testing is cumbersome and requires individuals to travel to their doctor and have blood drawn from their veins.

Dr Jackson said, “Patients and healthcare providers are often distant from pathology collection centres.”

As a result, most people taking oral anticoagulants only test their blood clotting time and adjust their medication dose once a month.

More regular monitoring equals better health outcomes

Portable devices for home testing make more regular INR monitoring and oral anticoagulant dose adjustment feasible. This is important because more regular monitoring considerably improves the health outcomes of individuals using oral anticoagulants. They are 50% less likely to experience stroke, heart attack or another adverse events caused by blood clots. They are also less likely to die from any cause or experience major bleeding.

Not all people can use a portable device for home monitoring. Some are unable to use the device (your doctor can advise if it is for you) and others don’t want to. For these people, it may be possible to test their blood and obtain instant results with a portable device at a health facility.

 Some people are able to not only monitor their INR but also use a pre-determined dose–INR schedule to make their own dose adjustments according to a predetermined dose INR schedule, avoiding the need to continually consult a doctor or go to a healthcare facility.

Prof Gallus said, “Patient self-testing and self-management allows patients to become more in-control of their own health and this will appeal to those who are motivated to self-help and manage their health.”

Dr Jackson said, “Patients who have sufficient dexterity to use a monitor (they are not dissimilar to a blood glucose monitor) and have sufficient knowledge of anticoagulation and the effects of warfarin are most likely to benefit from self-monitoring.”

He said that portable monitoring devices offer convenience and reduced communication errors.

Better INR monitoring, better health in Australia

INR monitoring with a portable device means better health for people on oral anticoagulants, as well as less inconvenience. It is a cost-effective method which is becoming routine practice in many developed countries.

Dr Jackson said, “The cost to the individual is greater if they own a monitor and do it themselves, but the total costs are much less with a portable INR monitor than with conventional laboratory testing.”

In Australia, portable devices have been tested and shown to be effective. Your doctor will be able to advice if they may be suitable for you.

Medicare rebates are not yet available to individuals who use this method of blood monitoring, although some private health funds do offer rebates.

More information


For more information, see Blood Clotting: International Normalised Ratio (INR).


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Posted On: 23 February, 2011
Modified On: 16 September, 2014


Created by: myVMC