About Warfarin

Warfarin is an oral anticoagulant medicine which is used to prevent blood clots forming in the circulatory system. The blood needs vitamin K to be able to clot and warfarin slows the production of vitamin K in the body which increases the time it takes for your blood to clot. Warfarin can take 2 -3 days to take effect and it will help the blood flow freely around the body. It does not eradicate clots that are already formed. Some people are at a greater risk of having a blood clot and clots can block vessels in the brain or heart causing a stroke or heart attack. Blood clots that form in the veins are known as deep vein thrombosis and sometimes a clot will travel from the leg to the lungs causing a pulmonary embolism.

Warfarin has to be monitored regularly and this is done by blood tests to check INR (international normalised ratio) levels. Monitoring usally takes place in dedicated anticoagualation clinics in hospital, at the GP surgery, Pharmacy or community setting.


Some people choose to  check their INR levels using a Coagulometer, a hand held device which measures and records the results.These  types of devices are often used in clinical settings. Self monitoring may be preferred for convenience and provide reassurance for warfarin users as they can test when they want to and the devices only need a pin prick of blood from the finger as opposed to a sample being taken from a vein.

The devices give an immediate INR reading, and patients can then notify the anticoagulation nurse or specialist of the result who will then advise of any dosing changes and when next to test. It is very important that you speak to your GP or Consultant if you wish to self monitor as they are responsible for ensuring your anticoagulation therapy is managed effectively. The  test strips for the devices  are available on the  NHS, however, there are some doctors who may not support self - testing as an option and therefore ACE always recommends you speak with your managing clinician before purchasing a device for this purpose.

In 2014, Nice produced guidelines for the use of these devices for people with Atrial Fibrillation and heart valve disease who require long term anticoagulation. For more information see  https://www.nice.org.uk/guidance/dg14