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PT/INR Test

Reasons to Get One, What to Expect, Associated Risks & More

Are you on long-term anticoagulant therapy? If so, you may need to take a prothrombin time (PT) test, which measures how long it takes the blood to clot. A PT test may also be called an INR (international normalized ratio), which standardizes the results of a prothrombin time test so that your doctor understands them – regardless of the testing method. The INR is used to determine the effects of oral anticoagulants, such as warfarin, on the clotting system.

So, why would a person be on an anticoagulant? Coagulation, or blood clotting, is a protective mechanism of the body that prevents you from bleeding when you get a cut or scrape. Normally, clotting only happens when there is blood loss from a damaged vessel, but there are several conditions that can cause blood clots to form, even in the absence of active bleeding. These conditions can put you at risk of thromboembolic disease – when fragments of blood clots block blood vessels in the lungs, heart, and brain, leading to pulmonary embolism, heart attack, or stroke. Anticoagulants are medicines that prevent these potentially fatal conditions by thinning the blood and reducing the chance of blood clots forming.

When on an anticoagulant such as warfarin, there is a delicate balance between making sure that the blood doesn’t clot and preventing excessive bleeding, which is why PT/INR testing is so important. The INR can be used to adjust a person’s drug dosage to get the PT into the range that is ideal for that person.

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If you’re preparing for a PT/INR test, it is important to know that there are many factors that can interfere with the results, so you should talk to your doctor beforehand if you:

  • Have a sudden change in diet, particularly eating more leafy greens
  • Are taking certain prescription and/or over-the-counter medications, such as aspirin or birth control
  • Are taking diet supplements, such as vitamin K
  • Are sick

One of the most convenient places to go for the PT/INR test is an urgent care clinic. You can use Solv to help you find out what the closest urgent care centers are to you, and which ones accept your insurance, before scheduling a same-day appointment at whichever one you choose.