Your Guide to INR Levels: What It Means, Why It’s Important

After you’re diagnosed with a blood clot, your healthcare provider may prescribe a blood thinner called warfarin. The doctor may also want to watch your INR levels over time. To do that, you’ll need regular blood tests.

While it may seem like a hassle to get blood work done, measuring INR levels helps your healthcare team make sure that you’re taking the right amount of warfarin. The goal of warfarin therapy is to reduce the blood’s tendency to clot. Too much warfarin may cause you to bleed too easily. If you don’t take enough, the drug won’t do its job.

What is an INR level?

INR stands for international normalized ratio. INR is simply a type of calculation. It’s used along with another measurement called prothrombin time (PT). Together, these tests help doctors understand what causes bleeding and clotting problems. 

What is a PT level?

PT stands for prothrombin time. Prothrombin is a protein produced by your liver. It helps your blood clot properly. PT time, also called or pro time, refers to how much time it takes for your blood to clot.

When you have a blood clot, which doctors call a thrombus, doctors measure PT using the INR. The INR number tells them how much time it takes for your blood to clot. That’s why it’s called a PT-INR test. 

Why do I need my INR levels checked?

Monitoring how well your blood clots with PT-INR tests helps doctors see if the warfarin you’re taking is working as well as it should. Your doctor may adjust your dose of warfarin depending on your INR levels.

Warfarin works by blocking substances in the blood that cause clotting. In other words, it helps prevent new blood clots. But warfarin can put you at higher risk of bleeding. Monitoring your PT-INR levels helps doctors check your bleeding risk.

What is a normal INR range? 

A normal PT-INR range for people who take warfarin is 2-3 but can vary from patient to patient. Patients who tend to clot more easily may have an INR target range of 3-4. Patients with a higher bleeding risk may have an INR level that’s between 2-2.5.

How often do I need a PT-INR test?

The American Heart Association recommends that people who take warfarin get their INR levels checked at least once a month. When you first start taking warfarin, or if your INR levels are too high or low, you may need tests more often. Some patients need testing as often as twice a week.

Where do I get a PT-INR test?

Most labs offer PT-INR tests. However, your doctor may refer you to a specialized clinic called an anticoagulation management service (AMS). These clinics specialize in taking care of patients on blood thinners. (Note: Blood thinners are also called anticoagulation medications.) The pharmacists at the AMS clinics can work with your doctor to adjust your medication as needed.

You can also do PT-INR tests at home. Home testing is available if you need to take warfarin for a long time. If you’re interested in home testing, talk to your doctor. You’ll need to learn how to use an INR monitoring machine and test strips.

What can I do to help keep my INR level where it should be?

Follow these tips to help keep your INR levels stable:

1. Listen closely to your doctor’s instructions and take your medication exactly as it’s prescribed. If you miss a dose, contact your doctor to find out how to safely restart it.

2.  Fill and refill your warfarin prescription at the same pharmacy. This helps ensure the brand of warfarin you’re on stays consistent. 

3. Make sure your doctor always has an up-to-date list of all the medications you take, including over-the-counter medicines. Some medications interact with warfarin. Even common drugs, like aspirin, acetaminophen (Tylenol), and some antacids and laxatives, can affect how well warfarin works.

4. Keep track of any foods you eat that contain vitamin K. Foods with high levels of vitamin K include kale, broccoli, and brussels sprouts.

Why pay attention to vitamin K? Foods high in vitamin K work against warfarin. When warfarin is less effective, your blood may clot more easily. When that happens your INR levels get lower.  

Other changes to your nutrition can also cause your INR level to rise and fall. Before starting a new diet or taking any new supplement, make sure to ask your doctor if it could affect your INR levels.

Do you need PT-INR tests? You have support.

Starting a new medication like warfarin can be challenging. Ask your doctor or your local pharmacist any questions you have about taking warfarin and getting PT-INR tests. If you’re referred to an AMS, the medical staff at those clinics can address any concerns.