Bleeding, blood in urine and stools, dizziness or weakness, severe bleeding such as a heavier menstrual period, severe headache or stomach pain, vision changes and head injury even if there is no bleeding (Medsafe, n.d.).

When taking warfarin, PT (measured as INR), will be checked every day until it is in the correct range. Once it is stable, the INR will be taken less often, such as every 2-3 weeks. After this, if it is stable it will be taken every 4-6 weeks (Health Navigator, 2020).

Prothrombin time measured as a ratio- INR. Because the results from the PT test vary from laboratory to laboratory, a INR is calculated. Calcculating it in this formula allows for differences in different laboratories so that the test results can be compared. In most cases the ideal target INR is between 2-3 but for some people at high risk of developing a blood clot the target needs to be higher - 2.5-3.5. If the INR is above target range, it means the blood is clotting too slow, which places a person at risk of bleeding. If it is lower than the target range, it means the blood is clotting quickly, putting the person at risk of developing unwanted clots (Health Navigator, 2020).

The PT test and INR test are both blood tests that measures how long it takes for the blood to clot. It is used to check blood disorders and to monitor blood thinning medications (Health Navigator, 2020).

Prothrombin time in seconds. Prothrombin is usually measured in seconds. It is the time it takes for your blood to clot. The results of the test vary depending on a number of factors. It depends on the laboratory, the test chemicals used in the different laboratories and the method that is used to test the blood (Health Navigator, 2020)