Before testing your INR at home, talk to your health care provider about what test results you should expect, and when you should contact them about your results.
Carefully read all instructions provided with your INR test meter.
The instructions will include a toll-free phone number that you can use to contact the manufacturer if you have questions about how to use the meter.
The following information is for patients and caregivers using an INR test meter at home.
How do I take blood from a fingerstick?
Always follow the instructions that came with your INR test meter and lancet. To get a successful blood sample:
- If your finger is cold, warm the finger to increase blood flow. This can be done by:
- Massaging the hand and the base of the fingers
- Holding the hand under the armpit
- Washing the hand with warm water
- Clean and dry the finger before sticking
- Do not squeeze or “milk” the finger
- If you are unable to get a sufficient amount of blood, you may need to switch to another area on the same finger, or switch to a different finger
How often should I use my INR test meter?
Follow your health care provider’s recommendations about how often you should perform the test, which is typically every 1–4 weeks. Be sure to talk with your health care provider before making changes to any of your medications, which could affect your warfarin dose or monitoring schedule. Also, be sure to tell your health care provider about any changes to your general health or diet because certain foods, such as leafy greens and some herbal supplements, can affect your body’s response to warfarin.
When should I contact my health care provider?
Monitoring warfarin at home with an INR test meter is convenient. However, there are risks associated with using INR test meters at home. If you experience any of the following situations while on warfarin, seek medical attention immediately:
- Sudden, unexpected bleeding (e.g. nosebleeds)
- Bleeding from an injury that you are unable to stop
- Blood in urine
- Blood in bowel movement (stool)
- Severe stomach pain
- Vomiting blood
- Bruising on your skin for no apparent reason
- Leg pain
- Shortness of breath
- Confusion, difficulty with speaking or understanding speech
- Weakness or numbness of the face, arms or legs
- Sudden vision loss
- Sudden, severe headache
- Trouble with walking, dizziness or loss of balance/coordination
- INR results >4.5 without signs or symptoms of bleeding
When should I be concerned about my INR results?
Your health care provider will identify the appropriate INR range when you are prescribed an INR test meter. If you obtain an INR result outside your identified target INR range, you should immediately contact your health care provider.
INR results above 4.5 are less reliable than results lower than 4.5. If you obtain an INR result above 4.5, your health care provider may want you to have your blood drawn and tested by a laboratory to make sure your INR test result is accurate, and you are receiving the appropriate warfarin dosage.
What could affect my INR results?
Certain changes such as illness or an increase in leafy green vegetables in your diet can cause a change in your INR test results. A variety of factors can cause an INR test meter to provide inaccurate results. These may include:
- Faulty test strips, caused by not storing test strips according to the manufacturer’s instructions
- Not storing, maintaining or cleaning the meter according to the manufacturer’s instructions
- Not following the manufacturer’s instructions for blood sampling, for example:
- Using a blood sample that is too small or too large
- Waiting too long to test after taking a fingerstick
- Squeezing the finger to “milk” drops of blood
- Moving the meter while testing is in progress or not using it on a stable surface
- Using previously owned test strips or test strips not authorized for sale in the United States.
Different meters use different technology to generate results. It is important to talk to your health care provider about your meter, and understand which health conditions and other factors may affect how it works. For example, common situations that may affect some meters more than others include:
- Having certain medical conditions such as anemia, infection and cancer
- Certain medications, for example some antibiotics
- Environment: humidity, altitude and temperature
Detailed information on meter-specific limitations can also be found in the limitation/warning sections of the user manual and instructions for use.
How can I ensure my INR test meter is working properly?
There are a few ways to ensure your meter is working properly:
- Ask your health care provider to periodically compare your INR test meter results with the results from a laboratory test. If possible, your health care provider should use the same laboratory each time for consistency.
- Perform quality control testing. Quality control test strips or liquid control solutions may be purchased to ensure your meter is working properly. Follow the manufacturer’s instructions to test with these products:
- Every time you open a new lot of test strips
- If you drop your test meter
- Whenever you obtain a result outside the range determined by your health care provider
- Electronic checks. Every time you turn on your meter, it performs an electronic check. If it finds a problem, it will display an error code. Look in your user manual to see what the error code means and how to fix the problem. If you are unsure, call the manufacturer’s toll-free number provided in the instructions and contact your health care provider.