Medical Questions » Pathology Questions » Question No. 784
| Question: | I have been told to take warfarin tablets life long as my heart beats irregularly, but I have to have blood tests every couple of weeks. What are these tests for? |
| Answer: | A clotting or coagulation test measures how long it takes the blood to clot. This test may be ordered for someone who bruises or bleeds excessively to find out if they are a sufferer from an hereditary disease such as haemophilia (in which the blood does not clot and so even a minor accident can cause excessive bleeding), or one of the many other diseases that can reduce clotting.
Patients with a high risk of blood clots forming in the heart, an artery or vein, which may result in a heart attack, lung damage or stroke, may be placed on anticoagulant drugs such as warfarin. Clotting tests are carried out regularly to monitor the effect of these drugs and to ensure that a balance is maintained between preventing a clot forming and stopping the blood clotting at all.
These tests are often reported as a ratio (international normalised ratio— INR) which measures how much longer the patient takes to stop bleeding than normal. A person with an INR of 3 takes three times as long to stop bleeding as a normal person. The doctor will determine the INR which is desirable for the patient (usually between 2 and 3-5), depending upon their diagnosis.
Warfarin may be life-saving in the correct dose, but if too much or too little is taken, there may be excessive internal bleeding, or the drug may not act to prevent dangerous blood clots in arteries. This is why regular blood tests are essential.
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