Which of the following diagnostic tests is used to monitor the effectiveness of warfarin therapy?

When trying to decide which testing device or IDTF service to use, you may want to consider:

• The advice or recommendation of your physician or anticoagulation clinic, based on their experience and knowledge.
• The experience of other patients and their satisfaction with their home monitoring device and the educational and support services provided to them by the manufacturer and/or distributor.
• The amount of blood needed for the test strip.
• Ease of use associated with operating the instrument or testing device.
• Weight of the instrument may matter to you, especially if you travel frequently.

If you are on warfarin and are interested in checking your INR with a home monitoring device, you should discuss your options with your healthcare provider. Your healthcare provider will need to 1) write a prescription for the device 2) be available to instruct you in dosage adjustments and 3) remain medically responsible for your anticoagulation management.Once a prescription has been written that directs you to self-test your INR, you can speak with your doctor or your insurance company for guidance about where to obtain your device and how to get started.

You also can get similar guidance from a POC device manufacturer or an Independent Diagnostic Testing Facility (IDTF) or distributor that provides patient services connected to at-home INR testing. Most of these IDTFs will require that your doctor send them your self-testing prescription, as well as your relevant medical information, to enroll you in their service.

IDTFs can play a valuable role in your self-testing efforts, as they can help you verify your insurance or Medicare coverage, provide training to help improve your self-testing skills, help manage your testing results, and ensure that your test results routinely reach your healthcare professional.

Below is an alphabetical listing of several different device manufacturers, IDTFs, and patient services that you can explore for more information and guidance:

Acelis Connected Health

Acelis Connected Health, an Abbott Company, provides an end-to-and service for PT/INR management with support for both patients and their physicians. You can learn more about Acelis Connected Health and their service by reading the frequently asked questions that appear on their website here.

Advanced Cardio Services

Advanced Cardio Services is an IDTF that provides a home anticoagulation testing and monitoring service to help reduce the risk of potential complications associated with long-term warfarin therapy or out-of-range INR levels. You can learn more about INR self-testing through this service by reading the frequently asked questions that appear on their website here.

CoaguChek® and CoaguChek® Patient Services

CoaguChek® and CoaguChek® Patient Services is a service of Roche Diagnostics. Roche Diagnostics manufactures and sells a broad spectrum of diagnostic equipment and supplies, including the CoaguChek® XS device for INR self-testing. To learn more about this company’s INR self-testing devices and patient home-testing services, you can begin by reading the information that appears on their CoaguChek® Patient Services website here.

mdINR

mdINR is a Lincare company, and an IDTF that provides equipment and services for patients who perform INR at-home self-testing. You can learn more about their services by reviewing the frequently asked questions posted to their website here.

RCS (Remote Cardiac Services)

RCS is an IDTF that supports the INR self-testing needs of clinicians and patients. You can learn more about INR self-testing through this service by reading the frequently asked questions that appear on their website here.

Remote INR™ by BioTel® Heart

Remote INR™ by BioTel Heart® (formerly CoaguChek® Patient Services) provides the convenience and quality to implement a successful self-testing anticoagulation program for patients and physicians. For more information about this company’s patient home-testing services, and to review the frequently asked questions that appear on their website, click here.

Warfarin is an oral anticoagulant used in the UK. Oral means it's taken by mouth. An anticoagulant is a medicine that stops blood clotting.

Clotting (thickening) is a complex process involving a number of substances called clotting factors.

Clotting factors are produced by the liver and help control bleeding. They work with cells that trigger the clotting process (platelets) to ensure blood clots effectively.

To produce some of the clotting factors, the liver needs a good supply of vitamin K.

Warfarin blocks one of the enzymes (proteins) that uses vitamin K to produce clotting factors. This disrupts the clotting process, making it take longer for the blood to clot.

When warfarin is prescribed

Anticoagulant medicines, such as warfarin, are often prescribed for people who've had a condition caused by a blood clot, such as:

Warfarin may also be prescribed for people at an increased risk of developing harmful blood clots, such as those with:

• a replacement or mechanical (prosthetic) heart valve
• an irregular heart rhythm, known as atrial fibrillation
• a blood clotting disorder, such as thrombophilia
• an increased risk of blood clots following surgery

Taking warfarin

It's very important that you take warfarin exactly as directed. Don't increase your prescribed dose unless the doctor in charge of your care advises you to.

Warfarin is taken once a day, usually in the evening. It's important to take your dose at the same time each day, before, during or after a meal.

The aim of warfarin therapy is to decrease the blood's tendency to clot, but not stop it clotting completely. This means the dose of warfarin you're taking must be carefully monitored and, if necessary, adjusted.

You'll have regular blood tests at your GP surgery or local anticoagulant clinic to make sure your dose is correct.

The international normalised ratio (INR) is a measure of how long it takes your blood to clot. 

The longer it takes your blood to clot, the higher your INR. Your INR will be used to determine the dose of warfarin you need to take.

Although there are now 3 new anticoagulants that don't require regular monitoring – rivaroxaban, apixaban and dabigatran – most people who need an anticoagulant will be prescribed warfarin.

When you start taking warfarin, you may be given a yellow booklet about anticoagulants, which explains your treatment.

How long you'll need to take warfarin for will depend on the condition for which it's been prescribed. Ask the healthcare professional responsible for your care if you're not sure.

Missed doses

If you usually take warfarin in the morning and forget to take it at your normal time, take it as soon as you remember and continue as normal.

However, if it's time to take your next dose, don't take a double dose to catch up, unless your GP has specifically advised you to.

If you forget to take your dose of warfarin in the evening but remember before midnight on the same day, take the missed dose.

If midnight has passed, leave that dose and take your normal dose the next day at the usual time.

Ask your GP or staff at your local anticoagulant clinic if you're not sure what to do about a missed dose of warfarin. You can also call NHS 24 111 service for advice.

Who shouldn't take warfarin

The following people shouldn't take warfarin:

Bleeding is the main side effect associated with warfarin, as it slows down the blood's normal clotting ability.

You're at greatest risk of bleeding in the first few weeks of starting treatment with warfarin and when you're unwell.

You should therefore seek medical attention if you:

• pass blood in your urine or faeces
• pass black faeces
• have severe bruising
• have long nosebleeds – lasting more than 10 minutes
• have bleeding gums
• cough up blood or have blood in your vomit
• experience unusual headaches
• have heavy or increased bleeding during your period, or any other bleeding from your vagina (in women)

Take extra care to avoid cutting yourself while taking anticoagulant medication because of the risk of excessive bleeding.

For example, you should:

• take care when shaving and brushing your teeth
• wear protective clothing when gardening, sewing or playing contact sports
• use insect repellent to avoid insect bites or stings

Seek urgent medical attention if you're taking warfarin and you:

• have a fall or accident
• experience a significant blow to your head
• are unable to stop any bleeding
• have signs of bleeding, such as bruising

Skin rashes and hair loss are also common side effects of warfarin.

Contact your GP or the healthcare specialist responsible for your care if you experience any persistent side effects while taking warfarin.

Interactions

Medicines

Warfarin can interact with many other medicines. The patient information leaflet that comes with a medicine should tell you if it's safe to take with warfarin.

Ask your GP or pharmacist if you're unsure.

When taking warfarin:

• don't take aspirin, or treatments containing aspirin, unless it's prescribed by a healthcare professional as it could cause bleeding 
• don't take ibuprofen unless it's prescribed by a healthcare professional
• you can take paracetamol, but don't take more than the recommended dose

Herbal medicines and supplements can also interact with warfarin. You should therefore avoid taking them without first checking with your GP, pharmacist, or staff at your local anticoagulant clinic.

Food and drink

Some food and drink can interfere with the effect of warfarin if consumed in large amounts, including foods that are rich in vitamin K.

Foods containing large amounts of vitamin K include:

• green leafy vegetables, such as broccoli and spinach
• vegetable oils
• cereal grains

Small amounts of vitamin K can also be found in meat and dairy foods.

When your first dose of warfarin is prescribed, it doesn't matter how much vitamin K you're eating because the dosage will be based on your current blood clotting levels.

However, if you make significant changes to your diet, such as increasing your vitamin K intake or cutting out foods that contain vitamin K, it could interfere with how warfarin works.

Consult the healthcare professional responsible for your care before making any significant changes to your diet while taking warfarin. They'll also be able to give you more information about foods to avoid or limit.

Alcohol

Getting drunk or binge drinking is dangerous while taking warfarin. It may increase the effect of the drug, increasing the risk of bleeding.

The latest guidelines on drinking alcohol state that regularly drinking more than 14 units of alcohol a week (for both men and women) risks damaging your health.

Fourteen units is equivalent to six pints of average-strength beer or 10 small glasses of low-strength wine.

Heavy drinkers or people with liver disease who are taking warfarin shouldn't drink alcohol.

Other useful information

Surgery and dental work

Because of the risk of bleeding, your dose of warfarin may need to be lowered or stopped a few days before having an operation or dental work.

Tell the surgeon or dentist that you're taking warfarin. You should also tell anyone else involved with your care, such as an anticoagulant nurse, if you need an operation so they can make arrangements.

Having vaccinations

You can have vaccinations while taking warfarin, but all injections must:

• be given under the skin
• not be given into the muscle as it may cause bruising 
• have firm pressure applied to the site for 10 minutes afterwards 

Playing sports

You can play sports while taking warfarin, but because of the risk of bleeding:

• contact sports that could lead to a head injury, such as football, rugby, cricket and hockey, are best avoided if played competitively
• martial arts and kickboxing must be avoided

You can continue to take part in non-contact sports, such as running, athletics, cycling and racquet sports. However, make sure you wear protective clothing, such as a cycle helmet.

Going on holiday

Tell your GP or anticoagulant nurse if you're going on holiday, in this country or abroad, and arrange to have your INR checked before you go.

If you're going to be away longer than a month, you may need to arrange to have your INR checked while you're away. Make sure you have enough warfarin tablets to last for the duration of your trip.

Body piercings

Body piercings aren't recommended while taking warfarin because of the increased risk of bleeding and risk of infection.