What Does a High INR Mean?

Warfarin (Coumadin) is an older blood thinner medication that has been around for a while. There are newer blood thinners that have become more popular. But for some people, warfarin is still the preferred medication to prevent blood clots.

One of the downsides of warfarin is that you need to get frequent blood tests to check something called an international normalized ratio (INR). People who take warfarin have a target INR range that shows their warfarin is at the right level in the body. If it’s too low, they’re at increased risk for blood clotting. But if it goes too high, they’re at increased risk of bleeding. So it’s important to know what to do if your INR level is high.

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): This measures how many seconds it takes for your blood to form a clot. As a reference, a normal PT value is between 11 and 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. 

What causes a high INR?

There are a lot of factors — beyond your warfarin dose — that can increase your INR level. This is one of the reasons people need to periodically measure their INR when they’re taking warfarin.

Causes of a high INR include:

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

• Medications: Many medications can affect the way your body processes warfarin. This can lead to a buildup of warfarin — and a high INR. 

• Diet: Food can affect your INR level too. 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.

• Supplements: Some supplements might have vitamin K in them. Other supplements — like St. John’s wort — can change the way your body processes warfarin. 

• Alcohol: Drinking alcohol can cause both a high and low INR. A night of heavy drinking can cause a high INR. Daily, long-term drinking can have the opposite effect.

What are the symptoms of a high INR?

Most of the time, people won’t have any symptoms when they have a high INR. But the problem with a high INR is that it can lead to serious bleeding. Here are some symptoms to watch out for:

• Abnormal skin bruising or bleeding from a wound 

• Nosebleeds, which can be life-threatening if your INR is too high

• A sudden or severe headache — a possible symptom of bleeding in the brain — which can happen on its own, after a head injury

• Red, purple, or black stool, which can be a sign of bleeding in the stomach or intestine

• Red or pink urine, which 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’ll go through this in more detail below.

How to interpret INR results

A normal INR is between 0.8 and 1.1. So anything above that is high. But if you’re taking warfarin, you want your INR to be higher than normal.

The higher the INR number, the “thinner” the blood. Someone’s target INR on warfarin will depend on why they need to take a blood thinner. But most people who take warfarin aim for an INR range between 2 and 3, or between 2.5 and 3.5.

So, a “high” INR for one person may be within the target range for someone else. 

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

When your INR is higher than it should be, there are a few different solutions. And you and your healthcare team 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 

If you’re not bleeding, your healthcare team will give you specific instructions on what to do if your INR is high. But the following guidelines can help you know what to expect:

• If your INR is 4 or less, you probably don’t need any specific treatments. You’ll 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 need treatment with vitamin K while holding off on taking your medication for a few days.

If you’re bleeding and your INR is high, this is a medical emergency. Anyone in this situation should be treated in an emergency room. They may need medications that help reverse the effect of warfarin: 

• 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.

How to prevent a high INR

Here are things to do to prevent a high INR:

• Consistency is key. Take your warfarin at the same time each day, and be sure to follow the prescribed dose. Don’t take extra doses without consulting with your healthcare team.

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

• Limit your alcohol use. 

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

Even if you do everything right, an INR level can still get too high or too low. It isn’t always easy to predict how the body will process warfarin. This is why it’s important to follow your INR testing schedule, even if your INR level has been stable. 

How to test INR at home

To test your INR at home, you’ll need a prescription from a healthcare professional. You should always do the following:

• Use an FDA-approved testing kit.

• Follow the instructions on how to test that’s included with your testing kit.

• Interpret the results with the guidance of your healthcare team.

Home testing kits for INR include a portable monitor, test strips, and a lancet. They require a finger prick — similar to the way people test their blood sugar. Different testing codes may have slightly different directions. But these are the basic steps to test your INR at home:

• Make sure your finger is warm. You can use warm water, your armpit, or massage to warm it up.

• Clean and dry your hands and fingers.

• Insert a test strip into your monitor. 

• Prick your finger with the lancet. Don’t squeeze or “milk” the finger.

• Apply a drop of blood to the strip within 15 seconds.

• The meter will provide a result in about a minute.

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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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