Why monitor warfarin use?
Staying on top of your PT/INR helps you stay healthy
If you are taking warfarin, then PT/INR, or INR, testing is a required part of your ongoing therapy. PT stands for “prothrombin time,” the time it takes for blood to clot. INR stands for “international normalized ratio,” a calculation for making results consistent no matter what type of test was used.
Your PT/INR results let your doctor know whether you’re taking the right amount of warfarin to keep you in range and on track. Testing is a continual commitment between you and your doctor. However, once you know your options, you’ll see how it can become a simple part of your routine.
Learn how warfarin works
Often called blood thinners, anticoagulants like warfarin (also called Coumadin®) help increase the time it takes for your blood to clot.1 For instance, if you’re taking warfarin and you cut your finger, it may take longer for the bleeding to stop than for somebody who isn’t taking an anticoagulant.
While several types of anticoagulants are available, warfarin is the most widely used blood thinner in the world.2
How warfarin works
Vitamin K plays a key role in forming clotting factors, which causes the blood to clot. Warfarin blocks the formation of vitamin K-dependent clotting factors, which helps prevent and slow the formation of harmful clots.
Who takes anticoagulants?
If you just found out from your doctor that you need to start taking warfarin, you’re not alone. Every day, millions of people worldwide take anticoagulants.3 They are commonly prescribed for or as a result of:4
• Atrial fibrillation (irregular heartbeat)
• Mechanical heart valves
• Venous thromboembolism
• Thrombophilia (tendency to cause blood clots)
• Heart attack (causing damage to heart muscle)
1 http://www.stoptheclot.org/learn_more/blood_clot_treatment.htm (accessed January 2018).
2 Wardrop, D. et al. (2008). British Journal of Haematology 141:757-763.
3 http://www.ismaap.org/welcome-detail/management-of-longtime-anticoagulation/ (January 2018)
4 Ryan, J. et al. (2008). Journal of Clinical Pharmacy and Therapeutics 33:581-590
5 Fiumara, K. et al. (2009). Circulation 119:e220-e222.
If you have any questions about PT/INR, talk to your doctor.
Keeping your PT/INR in range is key
When you’re prescribed warfarin, regular blood tests are required to ensure your blood isclotting within a target range.1 This is called PT/INR, or INR, monitoring.
An INR test shows how quickly your blood will clot while you’re on your current dose of warfarin, which helps determine whether your dose needs to be adjusted.
Your individual target range may vary based on disease state and advising doctor’s treatments.
For more information on your range, please contact your doctor.
1 American Heart Association, “A patient’s guide to taking warfarin,” http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/A-Patients-Guide-to-Taking-Warfarin_UCM_444996_Article.jsp (accessed January 2018).
2 Levi, M. et al. (2009). Seminars in Thrombosis Hemostasis 35:527-542.
There are three ways to test your PT/INR
All three ways provide accurate results. However, many warfarin patients choose self-testing for the freedom and convenience it offers.
Compare testing options
Think about which option works best for you and your lifestyle. All three options provide accurate PT/INR results.
1 The CoaguChek XS system may be used up to a maximum altitude of 14,000 feet. Internet availability required for wireless reporting. 2net™ Hub transmitter works only in the United States and requires a reliable cellular connection.
Learn how certain foods can impact your PT/INR
Like other medications, warfarin can be affected by what you eat and drink. While no foods are off limits, there are three important factors you need to consider.
1 Blood Thinner Pills: Your Guide to Using Them Safely. Agency for Healthcare Research and Quality, Rockville, MD. September 2015. Available at https://www.ahrq.gov/sites/default/files/wysiwyg/patients-consumers/diagnosis-treatment/treatments/btpills/btpills.pdf (Accessed January 2018.)
2 USDA. (Last modified May 2016). USDA National Nutrient Database for Standard Reference, Release 28, Vitamin K Content of Selected Foods (accessed January 2018).
3 American Heart Association. “A patient’s guide to taking warfarin.” http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/A-Patients-Guide-to-Taking-Warfarin_UCM_444996_Article.jsp (accessed January 2018).
4 Renaud, S.C. and Ruf, J.C..(March 15, 1996). “Effects of alcohol on platelet functions.” Clinica Chimica Acta 246(1-2):77-89. http://www.ncbi.nlm.nih.gov/pubmed/8814972 (accessed January 2018).
5 Coumadin (warfarin sodium) [package insert 293US11PBS01503]. (2011). Princeton, NJ: Bristol-Myers Squibb.
6 Agency for Healthcare Research and Quality, Rockville, MD. (August 2010). “Blood Thinner Pills: Your Guide to Using Them Safely.”, http://www.ahrq.gov/patients-consumers/diagnosis-treatments/btpills/btpills.html#using (accessed January 2018)
7 Mayo Clinic. “Warfarin side effects: Watch for interactions.” http://www.mayoclinic.org/diseases-conditions/deep-vein-thrombosis/in-depth/warfarin-side-effects/art-20047592?pg=2 (accessed January 2018).
What is coagulation?
Coagulation is the formation of blood clots inside the body. Proteins in the blood, called fibrins, and small elements in the blood, called platelets, work together to form a clot, which helps stop bleeding when you have a cut or injury.
What are anticoagulants?
Oral anticoagulants (blood thinners) such as warfarin or Coumadin® are drugs that help thin the blood of patients with conditions such as atrial fibrillation, thrombophilia and other diseases that increase the risk of forming blood clots. Patients taking warfarin have to sometimes make a lifelong commitment to this medication to avoid complications such as stroke or pulmonary embolism (blockage in the main lung artery).
These drugs are called vitamin K antagonists, and each patient reacts to them differently. There are also external factors that could interfere with the medication, including certain foods, stress and alcohol. That is why it is so important for anticoagulation patients to test according to a prescribed testing frequency.1
Why do I need warfarin?
For some people, blood clots form too easily, or they don’t dissolve properly. These clots can impede blood flowing through the body, potentially leading to heart attack or stroke.2 Anticoagulation medication such as Coumadin® or another brand of warfarin slows down the clotting process to help keep you in a safe range.
What is PT/INR?
PT stands for “prothrombin time,” or the time it takes for blood to clot. INR is short for “international normalized ratio.” This is a calculation for standardizing results from PT tests. Essentially, PT/INR is a measure of whether your blood is clotting at a safe rate. You may see this referred to as PT monitoring, INR monitoring, or PT/INR.
What health conditions require PT/INR testing?
Any condition that results in an increased risk for blood clots and is treated with warfarin (sometimes known as Coumadin® or other brand names) will require regular testing. These include:3
- Atrial fibrillation – The most common type of arrhythmia or irregular heartbeat.
- Venous thromboembolism (VTE) – Involving blood clots in the veins of the legs or the lungs; includes deep vein thrombosis (DVT) and pulmonary embolism (PE).
- Mechanical heart valves – Implantable devices, especially those with manmade surfaces, can cause blood clots to form.
- Thrombophilia – An increased tendency to form abnormal blood clots.
What’s the target range of PT/INR?
The goal of monitoring your warfarin dose is to remain in the target range recommended by your doctor. For most people, a result of 2.0 to 3.0 is appropriate, although those at higher risk of clotting may have a target range of 2.5 to 3.5.4 Talk to your doctor about the appropriate range for you.
What if my results are out of range?
If your INR is higher than the target range, blood clots may not form quickly enough, and you may experience bruising or be at increased risk of bleeding. If your PT/INR is too low, you may still be at risk of excessive clotting.4
What can affect my PT/INR level?
Many things can alter your PT/INR, including stress, missing a warfarin dose, taking herbal supplements and other medications, and consuming certain foods and beverages, such as kale and cranberry juice. Talk to your doctor about what’s appropriate for you.
Can I drink alcohol while taking warfarin/Coumadin®?
Alcohol can increase the effect of warfarin and further slow your clotting rate, causing your INR to be too high. You may want to avoid it while on warfarin.5 Talk to your doctor about what’s appropriate for you.
What’s the importance of vitamin K?
Warfarin works by blocking the body’s ability to use vitamin K, a necessary component in the formation of blood clots. When you’re taking warfarin, it’s important to keep the amount of vitamin K in your diet consistent, or it may impact the effectiveness of your warfarin doses.5
What foods are high in vitamin K?
Green vegetables such as spinach, kale and broccoli are high in vitamin K,6 as are the following foods:
- Green tea
- Beef and chicken liver
- Blueberries and blackberries
How often should I test?
Test frequency should be determined by your doctor.
1 Coumadin® (warfarin sodium) package insert revised October 2011.
2 American Heart Association. “What is excessive blood clotting (hypercoagulation)?” http://www.heart.org/HEARTORG/Conditions/More/What-Is-Excessive-Blood-Clotting-Hypercoagulation_UCM_448768_Article.jsp (accessed January 2018).
3 Ryan, J. et al. (2008). Journal of Clinical Pharmacy and Therapeutics 33:581-590.
4 American Heart Association. “A patient’s guide to taking warfarin,” http://www.heart.org/HEARTORG/Conditions/Arrhythmia/PreventionTreatmentofArrhythmia/A-Patients-Guide-to-Taking-Warfarin_UCM_444996_Article.jsp (accessed January 2018).
5 Blood Thinner Pills: Your Guide to Using Them Safely. Agency for Healthcare Research and Quality, Rockville, MD. September 2015. Available at https://www.ahrq.gov/sites/default/files/wysiwyg/patients-consumers/diagnosis-treatment/treatments/btpills/btpills.pdf (Accessed January 2018.)
6 Mayo Clinic. “Warfarin diet: What foods should I avoid?” http://www.mayoclinic.com/health/warfarin/AN00455 (accessed January 2018).