Learn more about laboratory tests, reference ranges, and understanding results. The information on this site should not be used as a substitute for professional medical care or advice.
Contact a health care provider if you have questions about your health. What is it used for? Warfarin is a blood-thinning medicine that's used to treat and prevent dangerous blood clots. Coumadin is a common brand name for warfarin. The test may be done on a blood sample from a vein or a fingertip. For a blood sample from a vein: A health care professional will take a blood sample from a vein in your arm, using a small needle. For a blood sample from a fingertip: A fingertip test may be done in a provider's office or in your home.
During this test, you or your provider will: Use a small needle to puncture your fingertip Collect a drop of blood and place it onto a test strip or other special instrument Place the instrument or test strip into a device that calculates the results.
At-home devices are small and lightweight. Will I need to do anything to prepare for the test? Are there any risks to the test? What do the results mean? If you are taking warfarin: INR levels that are too low may mean you are at risk for dangerous blood clots. INR levels that are too high may mean you are at risk for dangerous bleeding. Your health care provider will probably change your dose of warfarin to reduce these risks.
If you are not taking warfarin and your INR or prothrombin time results were not normal, it may mean one of the following conditions: A bleeding disorder, a condition in which the body can't clot blood properly, causing excessive bleeding A clotting disorder, a condition in which the body forms excessive clots in arteries or veins Liver disease Vitamin K deficiency.
Vitamin K plays an important role in blood clotting. Your healthcare provider uses the INR to know whether your anti-clotting medicines are at the right dose or if you need to change the dose.
Newer anti-clotting medicines don't need INR monitoring and dose changes like warfarin does, so this lab test may not be used for those medicines. You may also need this test to help your healthcare provider diagnose and manage certain health problems, such as liver disease and bleeding disorders.
Your healthcare provider will order the PT test first, so that the results can be used to calculate the INR. In a PT test, chemicals are added to your blood sample, and the lab measures the time in seconds that it takes to clot. Your provider may also order these tests if he or she is concerned about your liver function or risk of bleeding:.
Test results may vary depending on your age, gender, health history, the method used for the test, and other things. Your test results may not mean you have a problem.
Ask your healthcare provider what your test results mean for you. The INR is a ratio, so it's just a number, not a number tied to time or another value. Your results will vary according to your age, the medicines you take, and any health problems you have. In general, the higher the number, the longer it takes for your blood to form a clot. Your INR number should be between 2 and 3 if you are taking a blood thinner, but it could be different, depending on your condition.
For instance, your INR goal if you are being treated for a mechanical heart valve will be different than your INR for a clot in your leg. The INR goal is usually higher for mechanical heart valves, especially the mitral valve.
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