Warfarin is a blood thinner, and the PT/INR blood test shows how well warfarin is working to prevent blood clots by measuring how long a sample of your blood takes to form a clot. A result that is too low and one that is too high may mean opposite risks, so the first thing to find out is which way yours moved. A big change in what you eat is one possible explanation for either, because eating certain foods can change the way warfarin works. Depending on where you get care, the provider who manages your warfarin may be a doctor, nurse, physician's assistant, nurse practitioner, pharmacist or other health care professional, and whoever it is needs to hear about the change in your eating.
What an INR that is too low or too high may mean
An INR that is too low may mean you are at risk of dangerous blood clots, because your blood clots too easily, and an INR that is too high may mean you are at risk of dangerous bleeding, because your blood is taking longer than normal to form a clot. If your INR is not normal, the provider who manages your warfarin will probably change your dose, and to understand the result they will consider your symptoms, your medical history and the results of other blood tests. If nobody told you whether your result was too low or too high, ask that provider which it was.
Besides a missed dose, a result outside your range may be due to any of the causes below.
| Your INR | What it may mean | It may be due to |
|---|---|---|
| Too low: your blood is clotting too quickly | A risk of dangerous blood clots | A clotting disorder; supplements with vitamin K, or a diet high in vitamin K; certain medicines |
| Too high: your blood is clotting too slowly | A risk of dangerous bleeding | A bleeding disorder; liver disease; vitamin K deficiency |
Why a change in what you eat shows up in a blood test
Vitamin K plays an important role in blood clotting, and high amounts of vitamin K can work against warfarin, so how much of it you eat can show up in how quickly your blood clots. Other blood thinners are not affected by vitamin K, so if you take a different one, ask the provider who manages it whether your diet can affect how well it works.
Fewer greens on the plate is not automatically the safer direction. On warfarin the aim is not to change the amount of these foods you eat from day to day or week to week, and eating far fewer of them is a change too. A diet high in vitamin K is one of the possible causes of an INR that is too low, and vitamin K deficiency is one of the possible causes of an INR that is too high.
Other things that may affect your PT/INR result include alcohol, high-fat diets, soybean and canola oils, and foods high in vitamin K such as green leafy vegetables, and some medicines and supplements may affect it too. Tell the provider who manages your warfarin about a change in any of them. Alcohol itself is something to avoid while you are taking a blood thinner, so ask that provider about any drinking you do now.
Do you have to put your eating back the way it was?
Not on your own, because putting your eating back the way it was would be another big change. Before a major change in your diet or a new weight loss plan, check with the provider who manages your warfarin first. Your change came before that talk, so have it now, before your next test, and leave what the change means for your dose to that provider. Until then, aim for a steady amount: eat consistent amounts of vitamin K-containing food on a week-to-week basis.
You do not have to avoid the foods and products below. Try to eat or drink only small amounts of them, and at the least keep the amount you have the same from day to day and week to week:
- Mayonnaise and some oils, such as canola, olive and soybean oils
- Broccoli, Brussels sprouts and raw green cabbage
- Endive, lettuce, spinach, parsley, watercress, garlic and scallions (green onions)
- Kale, collard greens, mustard greens and turnip greens
- Cranberry juice and green tea
- Fish oil supplements
- Herbs used in herbal teas
When you call the provider who manages your warfarin, start with what changed in your eating and the week it began, then go through these:
- Any new vitamin or herbal product, such as a multivitamin, garlic, ginkgo biloba or green tea.
- Any product containing aspirin, which may lessen your blood's ability to form clots and may increase your risk of bleeding while you are taking a blood thinner.
- Any new medicine another doctor has ordered, a weight medicine included, because dose changes for your blood thinner may be needed (see A weekly weight medicine can change how some of your other tablets work).
- A request for a list of foods that contain vitamin K, which you can ask that provider or your pharmacist for.
- A question about what to avoid before your next PT/INR test.
If you are pregnant or breast-feeding
If you are pregnant or breast-feeding, tell the provider who manages your warfarin, and tell them as well if you suspect you are pregnant or plan to become pregnant while taking it. According to MedlinePlus's warfarin drug information, warfarin may harm a fetus. Talk with that provider about effective birth control while you take warfarin, and call that provider immediately if you become pregnant. If you take warfarin with a mechanical heart valve, talk with them about the risks and benefits of continuing warfarin during pregnancy.
Signs that cannot wait for the next appointment
After a fall or a hit to the head, call the provider who manages your warfarin and go to the hospital immediately, even if you are not bleeding, because you can be bleeding without seeing any blood, and after a blow to the head the bleeding can be inside your skull.
Bleeding is the most common side effect of a blood thinner. Any one of these signs of serious bleeding means calling the provider who manages your warfarin immediately:
- Menstrual bleeding that is much heavier than normal
- Red or brown urine
- Bowel movements that are red or look like tar
- Bleeding from the gums or nose that does not stop quickly
- Vomit that is brown or bright red
- Anything red in color that you cough up
- Severe pain, such as a headache or stomachache
- Unusual bruising
- A cut that does not stop bleeding
- A serious fall or bump on the head, which also means going to the hospital immediately
- Dizziness or weakness
A severe headache with no fall or blow behind it is on that list, so call that provider immediately; once there has been a fall or a hit to the head, go to the hospital as well, whether or not your head aches.
An INR that is too low may mean a risk of dangerous blood clots, so watch for the signs of a clot as well as the bleeding signs above. Symptoms of a clot in a vein, called venous thromboembolism, can include swollen and tender legs that are painful to the touch, when a clot blocks blood flow in a leg vein, and shortness of breath and pain when breathing, when a clot travels to the lungs. For shortness of breath or pain when breathing, go to the emergency room now or call 911, because those can be symptoms of a clot in the lungs; for a swollen, tender leg, call the provider who manages your warfarin, or another healthcare provider, right away. A clot in a vein sometimes causes no symptoms until serious complications develop, so feeling well is no reason to keep the change in your eating to yourself.
Warfarin's possible side effects include nausea, vomiting, diarrhea and loss of appetite, and each is a reason to call the provider who manages your warfarin immediately. Being unable to eat for several days, for whatever reason, is a reason to call that provider as well, because problems like these could affect your blood thinner dose.
If NicoCares handles your weight care, your care team there needs to know you take warfarin, and the provider who manages your warfarin needs to know about the weight care. The care team replies in Spruce, the messaging app you joined from an invitation Spruce emailed you, and the site sets no reply time, so act on any sign above the way that sign says, without waiting for one.
