What Does a High INR Mean?

Warfarin (Coumadin) is a common medication that people take to prevent their blood from clotting. And if you’re one of these people, you know that you need to get frequent blood tests to check your international normalized ratio (INR). This test indicates how long it takes your blood to clot. The higher the INR number, the longer it takes the blood to clot (or the “thinner” the blood). A “normal” INR is between 0.8 and 1.1 if you’re not taking any medications that prevent your blood from clotting (sometimes called “blood thinners”). 

People who take warfarin have higher INR levels because the medication slows the time it takes blood to clot. For most people who take warfarin, the target INR is between 2 and 3, or 2.5 to 3.5, depending on the indication. But that number often rises over the target range — even without any changes to your dosage. And this can put you at risk for dangerous bleeding. We’ll explain why this happens, what to do if it happens to you, and ways to prevent it.

What is a PT/INR test?

A PT/INR test is a blood test. These two values measure how quickly your blood clots: 

• Prothrombin time (PT): Thismeasures how many seconds it takes for your blood to clot. A normal PT value is between 11 and 13.5 seconds. If you’re taking warfarin (Coumadin) or other medications that affects how your blood clots, your PT will be longer than 13.5 seconds. 

• International normalized ratio (INR): This number is calculated from your PT. The INR gives information about how quickly your blood clots when compared to blood that clots normally. A normal INR value is between 0.8 and 1.1. If you’re taking medication that affects how your blood clots, your INR will be higher than 1.1.  

Why do you need a PT/INR test?

A PT/INR test measures how well you’re responding to warfarin (Coumadin) or another blood thinner. If your level is too low, you may need to increase your medication dose. If your level is too high, you may need to lower your medication dose. 

You may need a PT/INR test every few days or weeks until your levels reach your goal INR. Once your INR levels are within your target range, you will need this test less often.

How do you prepare for a PT/INR test?

You may not need to do anything to prepare for your PT/INR test. Sometimes, your healthcare provider will ask you to skip one or more doses of your warfarin (Coumadin) before your PT/INR test. If you need to skip doses, check with your provider to see if you should restart your medication as soon as you take your test or if you should wait until your results come back. 

What increases INR levels?

Sometimes it’s hard to keep your INR level within the target range. This is because there are a lot of factors — beyond your warfarin dose— that can increase the INR level. This is one of the reasons people need to repeatedly measure their INR when they’re taking warfarin.

Here are some reasons your INR level may increase:

• Changes in dose: A higher dose may lead to a higher-than-expected INR.

• Medications: Lots of medications can affect the INR. Changes to your other daily medications can affect the way your body processes warfarin. This can lead to a buildup of warfarin in your system and a high INR.

• Diet: Many foods can affect your INR level. Most of the time this is related to how much vitamin K is in your diet. Warfarin works by blocking the effect of vitamin K. So, if you decrease the amount of vitamin K in your diet, this could lead to a high INR. Some experts believe that grapefruit can also lead to a high INR by affecting how the body metabolizes warfarin. But there’s no hard evidence to prove this.

• Dietary supplements: Some supplements might have vitamin K in them, so changes to how you take these can affect the INR level.

• Alcohol: Drinking alcohol may lead to unpredictable changes in your INR.

• Herbal supplements: Many herbs can affect how your body metabolizes warfarin. St. John’s wort is a common example.

What are the symptoms of a high INR? 

Most of the time, people will not have any symptoms when they have a high INR. But the problem with a high INR is that it can lead to serious bleeding. Bleeding might be obvious, such as from a wound or a nosebleed. But there are some symptoms of bleeding inside the body to watch out for:

• Headaches might come from bleeding in the brain. This can happen on its own or because of a head injury.

• Red, purple, or black stool can be a sign of bleeding in the gastrointestinal tract.

• Red or pink urine can also be a sign of internal bleeding.

If you have any signs of bleeding with a high INR, get medical attention right away. We will go through this in more detail below.

Do you need to see a healthcare provider if your INR is high?

When your INR is high, there are a few different solutions. And you and your provider will come up with a plan to lower it. This plan will depend on two main factors:

• How high the INR level is

• If there are any signs of bleeding 

Bleeding can be a life-threatening condition. So the best advice is to head straight to the emergency room. There are medications that help reverse the effect of warfarin on the body. Here are some possible treatments you may receive while you’re there:

• Vitamin K can be given by mouth or as an injection. Vitamin K slowly lowers the INR, so this is a good option if the bleeding isn’t serious. Or it may be used along with some of the other treatments.

• Fresh frozen plasma is a part of blood that people have donated. It replaces important clotting proteins to help stop the bleeding. You may get this if you need your INR level lowered quickly.

• Prothrombin complex concentrate (PCC) also provides special proteins that help the blood to clot. PCC can rapidly lower the INR to normal. This is typically used when the bleeding is life-threatening.

If you’re not bleeding, a high INR might not be as much of an emergency. The healthcare provider who is prescribing your warfarin can tell you what to do. There isn’t a one-size-fits-all answer. But knowing the guidelines can be helpful if you’re waiting to talk to your provider:

• If your INR is 4 or less, you probably don’t need any specific treatments. You will likely skip a few doses of warfarin and let the INR lower on its own.

• If your INR is between 4 and 10, you might take some vitamin K and skip your medication for a few days.

• If your INR is higher than 10, you’ll probably take vitamin K. You’ll also want to stop taking warfarin and get frequent INR checks to make sure it’s improving.

Be sure to talk to your provider before changing your medication or taking vitamin K. They can help point you in the right direction and prescribe medications if you need them. 

How to prevent elevations in your INR

While you can’t always predict changes in your INR, consistency is key to keeping it as stable as possible:

• Follow the directions of your prescribed warfarin dosing. And take the medication around the same time every day.

• Pay attention to your diet, particularly the foods that contain higher levels of vitamin K (like leafy greens). 

• Limit alcohol use. 

• Talk to your provider before you start a new medication or supplement. Be sure to ask how this may affect your INR levels. This way you can arrange for closer monitoring until your body adjusts to the new medication. 

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Written by:

Michael Dreis, MD

Dr. Dreis is an emergency medicine physician currently practicing in Milwaukee, Wisconsin. He went to medical school at the University of Wisconsin – Madison and completed his residency at Henry Ford Hospital in Detroit, Michigan.

Edited by:

Katie E. Golden, MD

Katie E. Golden, MD, is a board-certified emergency medicine physician and a medical editor at GoodRx.

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