For more information, see Anticoagulants. What is the INR? Regular monitoring is important with a drug such as warfarin because: There is a very small difference between the lowest dose that gives a good effect and the highest dose before side effects which may be serious are experienced; The doses used by different individuals to achieve the same effect can be highly variable; Several drugs interact with the medication to either increase or decrease its effectiveness; and What a person eats can also affect the action of warfarin and either increase or decrease its effectiveness.
Therefore, you should consult your doctor if you: Have a sudden change of diet leafy greens in particular ; Are taking diet supplementation; Are unwell; or Are taking other medications, including over-the-counter medications.
Common medications that interfere with warfarin include: Many antibiotics ; Some heart medications, such as amiodarone e. Aratac , Cardinorm , diltiazem e. Cardizem , Diltahexal and propranolol e. Deralin , Inderal ; Some anti- cholesterol medications, such as simvastatin e. Lipex , Zocor ; Some pain relievers and anti-inflammatories, such as celecoxib Celebrex and tramadol e. Tramal , Zydol ; Some antidepressants , such as citalopram e.
Cipramil and sertraline Zoloft ; and Some antiepileptics , such as carbamazepine e. Laboratory testing Laboratory blood testing is the traditional practice in Australia. Testing using a portable device Portable devices, introduced in the s, allow you, your doctor or another health practitioner e. Health facility monitoring with a portable device If the device is used for monitoring in a health facility, a health practitioner often a nurse conducts the blood test and records the result on your behalf.
Home monitoring with a portable device When a portable device is used for home monitoring, you usually conduct the test yourself. Self-testing with a portable device If you self-test, there are two options available: Self-monitoring: which involves your testing your INR at home, and then phoning a clinic with the result and to find if there is a need to adjust the dose and if so what the dose adjustment is; or Self-management: which involves you testing your INR at home, and adjusting your oral anticoagulant dose based on the result obtained, according to a pre-determined dose INR schedule.
More information For more information on coagulation, including information on anticoagulants, blood coagulation tests and test devices, see Blood Clotting and Monitoring. References Tripodi A. Prothrombin time international normalized ratio monitoring by self-testing. Curr Opin Hematol. A critical evaluation of the prothrombin time for monitoring oral anticoagulant therapy. Pathophysiol Haemost Thromb. Self-monitoring and self-management of oral anticoagulation.
Cochrane Database Syst Rev. Antithrombotic drugs: Part I. Optimal oral anticoagulant therapy in patients with mechanical heart valves. N Engl J Med. An analysis of the lowest effective intensity of prophylactic anticoagulation for patients with nonrheumatic atrial fibrillation. Comparison of low-intensity warfarin therapy with conventional-intensity warfarin therapy for long-term prevention of recurrent venous thromboembolism.
Optimal frequency of patient monitoring and intensity of oral anticoagulation therapy in valvular heart disease. J Thromb Thrombolysis. Warfarin: Indications, risks and drug interactions.
Aust Fam Physician. Important Phone Numbers. Topic Contents Overview How can you care for yourself at home? When should you call for help? Where can you learn more? Top of the page. Overview You had a blood test to check how long it takes your blood to clot. How can you care for yourself at home? Be careful with medicines and foods Don't start or stop taking any medicines or natural health products unless you first talk to your doctor. Keep the amount of vitamin K in your diet about the same from day to day.
Do not suddenly eat a lot more or a lot less food that is rich in vitamin K than you usually do. Vitamin K affects how warfarin works and how your blood clots. Limit your use of alcohol. Avoid bleeding by preventing falls and injuries Wear slippers or shoes with non-skid soles. Remove throw rugs and clutter. Rearrange furniture and electrical cords to keep them out of walking paths. Keep stairways, porches, and outside walkways well lit.
When the INR is higher than the recommended range, it means that your blood clots more slowly than desired, and a lower INR means your blood clots more quickly than desired. Mayo Clinic does not endorse companies or products. Advertising revenue supports our not-for-profit mission. This content does not have an English version. This content does not have an Arabic version. Sections for Prothrombin time test About.
Overview The prothrombin time, sometimes referred to as PT or pro time test, is a test to evaluate blood clotting. Request an Appointment at Mayo Clinic. Share on: Facebook Twitter. Lab Tests Online. Accessed Oct. Feldman M, et al. Levels that are too high can cause dangerous clots to form in your arteries or veins. It also checks to see if a medicine that prevents blood clots is working the way it should.
A PTT test also checks for clotting problems. You may need this test if you are taking warfarin on a regular basis. The test helps make sure you are taking the right dose.
If you are not taking warfarin, you may need this test if you have symptoms of a bleeding or clotting disorder. It helps make sure your blood is clotting normally, so you won't lose too much blood during the procedure.
A health care professional will take a blood sample from a vein in your arm, using a small needle. After the needle is inserted, a small amount of blood will be collected into a test tube or vial. You may feel a little sting when the needle goes in or out.
This usually takes less than five minutes. A fingertip test may be done in a provider's office or in your home. During this test, you or your provider will:. If you are using an at-home test kit, you will need to review your results with your provider.
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