Tips for using INR test meters at home for patients and caregivers

There is a blood test known as a prothrombin time test (PT), which measures the amount of time for blood to clot. PT is known as the International Normalized Ratio (INR). The INR is calculated from the findings of a PT test and used to monitor individuals who are prescribed the anticoagulant medication warfarin.

Typically, people go to a clinic or a health care provider to do this test. However, it is possible to take the test at home. Before doing the INR at home, you should consult with your health care provider about the numbers and test results you should get and when or how to contact them if you have any problems. Read all instructions about your INR test meter that are provided in its box. You can also contact the manufacturer if you have questions with the toll-free phone number provided in the instructions. If you want to learn more about INR testing, check out our article about INR testing at home.

How to take blood from fingers?

Read the instructions that come with an INR test meter and lancet and follow them strictly. Here are some tips to get your blood sample:

  • Warm your fingertips in case they are cold. Warming your fingers increases blood flow. Do it by:
    • Massaging the tips of the fingers
    • Holding your hand under the armpit
    • Holding your hand under warm water
  • Before using the lancet, clean and dry the finger before.
  • Try not to squeeze your finger.
  • If you cannot get enough blood on your first try, you can switch to another area on the same finger or use another finger.


When should I use my INR test meter?

To understand how often you need to do the test, you can contact your health care provider and follow their recommendations. It is typically recommended to perform the test every 1 to 4 weeks. Consult with your health care provider if you want to make any changes to your medications because any change may affect your warfarin dose or monitoring schedule.

Certain foods like leafy green vegetables and some herbal supplements can influence your body’s response to warfarin. Therefore, you need to tell your health care provider if you are about to change your general health or diet.


When to contact a health care provider?

Like any other medical test, there are risks to monitoring warfarin at home with an INR test meter. When taking warfarin, seek medical attention immediately in the following situations:

  • Sudden bleeding, such as nosebleeds
  • The inability to stop bleeding from an injury
  • Existence of blood in the urine
  • Existence of blood in bowel movement
  • Intense stomach pain
  • Vomiting blood
  • Bruises on your skin
  • Leg pain
  • Shortness of breath
  • Having difficulty understanding speech or speaking
  • Feeling weak or numb in body parts, such as the face, arms, or legs.
  • Sudden visual loss
  • Intense headache
  • Feeling dizzy or loss of balance.
  • An INR result higher than 4.5 without any signs or symptoms of bleeding


When to concern about INR results?

When a doctor prescribes you an INR test meter, your health care provider will identify the appropriate INR range for you. Contact your health care provider if you get an INR result outside of your specified INR range.

An INR result higher than 4.5 is less reliable than a result less than 4.5. Therefore, in the case of an INR result higher than 4.5, you may be requested to have your blood drawn and tested by a laboratory to confirm the accuracy of your INR test result and your warfarin dosage.


What affects the INR results?

There are certain changes in your usual routine, such as illness or an increase in the intake of leafy green vegetables, that can result in a change in your INR test results. An INR test meter can provide inaccurate results due to a number of factors. These may include:

  • ِDefective test strips. It can be caused by storing test strips in poor conditions.
  • Storing, maintaining, or cleaning the meter in a way that does not abide by the manufacturer’s instructions.
  • Taking the blood sample against the manufacturer’s instructions:
    • Taking a too small or too large blood sample
    • Taking a fingerstick too long before testing
    • “Milking” drops of blood by squeezing the finger
  • Moving the meter when it is progressing or using it on an unstable surface
  • Using previously owned or unauthorized test stips for sale in the United States.

Every meter has its own different technology to generate results. Contact your health care provider before starting to use the meter. Learn about health conditions and other factors that affect how an INR meter works. For example, the following common situations may affect some meters:

  • Anemia, infection, cancer, and other medical conditions.
  • Antibiotics and other certain medications.
  • Humidity, temperature, and altitude.

Meters have user manuals with instructions and warnings in them. Read the manual, so you can understand how to use the INR meter properly.


Points to Consider Before Transitioning to Home Testing

There are a few more things to consider before moving on to home testing:

  • Before moving to home testing, you should get your INR checked at a lab or clinic a few times. Before you begin self-testing, your healthcare professional will need to ensure that your warfarin dosage is stable. Most insurance companies require patients to take warfarin and have lab tests for three months before moving to home testing. (During COVID-19, several plans waived this requirement.)
  • The insurance coverage for home testing varies per plan. Many insurance companies reimburse the cost of home testing; however, some patients may be required to pay a copay or other out-of-pocket expenses.
  • Most insurers also require you to test your levels every two weeks, with other policies requiring weekly testing. So, if you have previously had a blood draw once every month or every 6 weeks in past, you may need to test yourself 2 to 3 times more regularly – but the benefit is that you can do it at home. If the firms who offer the machines/training do not hear from you within a couple of weeks, they will remind you to submit your feedback.


Who Should Be Considered for In-Home Testing?

Patients, especially seniors, who can’t go to the lab regularly, travel frequently, have trouble leaving their homes, or wish to be more independent can choose in-home testing. Whatever your rationale for transitioning to home testing, the important thing is that you continue to test your levels.


When a patient expresses a desire for in-home testing, the reason for their anticoagulation must be considered. Some blood illnesses, such as antiphospholipid syndrome (APLS), interfere with how the system evaluates INR ratings. Therefore, point-of-care testing is preferred not to be conducted on those individuals.


How to be sure the INR test meter is working properly?

To ensure the proper function of the INR meter, you can use different ways:

  • Visit your health care provider and ask them to compare your test results from an INR test meter and a laboratory test. It is better if your health care provider uses the same laboratory each time for consistency.
  • Take quality control testing. In order to ensure your meter is functioning properly, quality control test strips and liquid control solutions can be purchased. The manufacturer has instructions about what to do with their products, such as:
    • Every time you want to use a new piece of test strips.
    • When you drop your test meter.
    • When you get a test result that is not in the determined range.
  • Electronic checks. Your meter does an electronic check when you turn it on. An error code will be displayed when there is a problem. Use the user manual to the meaning of the error code and how to fix it. If you cannot fix the problem or have questions, call the toll-free number of the manufacturer and contact your health care provider.


Let’s sum up …

The FDA has many regulations related to taking an INR test. Fortunately, patients do not need to visit their health care provider’s clinic every time they want to test their INR. You can perform your test at home using an individual INR test meter. Keep in mind that there are risks in doing this test at home. Patients must be aware of the risks and other factors which can alter the test results. It is recommended to talk to your health care provider before you start taking the test.

If you have used INR test meters at home, please tell us about your experience.

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