Using INR Test Meters at Home

What is Warfarin?

Warfarin (also known by the brand names Coumadin and Jantoven) is a blood thinner prescribed to prevent and treat blood clots. Warfarin therapy may be prescribed for patients with certain types of irregular heartbeat, blood clots in the legs or lungs, and patients who have certain medical device implants such as artificial heart valves. A patient’s warfarin dose depends on many factors, including the patient’s age, overall health and genetic makeup. The dose may also need to be adjusted based on a patient’s diet and current medications.  

Monitoring Warfarin

Warfarin must be monitored to ensure it is working effectively and being used safely. Achieving the correct warfarin dosage can be difficult but is extremely important. If the dose of warfarin is too low (thick blood), the patient is at risk of developing harmful blood clots. If the dose of warfarin is too high (thin blood), the patient may be at risk of serious bleeding. It can be monitored by drawing blood from a vein and sending the blood to an accredited laboratory to test, or it can be monitored by testing blood from a fingerstick with an INR test meter outside of a laboratory. An INR target range is set by a doctor or health care provider. It is typically between 2.0 and 3.0 for basic blood-thinning needs, though the range may vary based on a patient’s specific condition. An INR above the patient-specific target range may increase the risk of bleeding, while an INR below the target range may increase the risk of developing a blood clot. Patients should work with their doctor or health care provider to develop a plan for achieving and maintaining a target INR; recognize when there is a problem; and know when to contact their health care provider.  

What are prothrombin time (PT) & INR?

PT and INR are both measures of how long it takes your blood to clot, expressed in two different ways. PT stands for prothrombin time. It is a measure in seconds of how long it takes your blood to clot. The results of the PT test vary depending on the laboratory, the test chemicals used in different laboratories and the method used to test blood. To standardize the PT test, a ratio called the international normalized ratio (INR) is calculated. The INR is a formula that allows for differences between laboratories so that test results can be compared.  

What do your PT test results mean?

• A number higher than average means it takes blood longer than usual to clot. A lower number means blood clots more quickly than expected.
• A prolonged PT means that the blood is taking too long to form a clot. This may be caused by conditions such as liver disease, vitamin K deficiency, or a coagulation factor deficiency.

Prothrombin time as a ratio – INR

Because the results of the prothrombin time test vary from laboratory to laboratory, a ratio called the international normalized ratio (INR) is calculated. The INR is a formula that allows for differences in different laboratories so that test results can be compared.  

What do your INR results mean?

For people taking warfarin, the INR target range will be different for different people, depending on the condition for which the warfarin is being prescribed. In most situations, the target INR is between 2 to 3. For some who have a high risk of a blood clot, the INR needs to be higher – about 2.5 to 3.5. If your INR is above the target range, this means that your blood is clotting too slowly and you are at risk of bleeding. If your INR is below the target range, this means that your blood is clotting more quickly than ideal (for people on warfarin) and you may be at risk of unwanted clots being formed. When your INR is out of range, your doctor will advise you on how to adjust your warfarin dose.  

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: Washing the hand with warm or hot water Massaging the hand and the base of the fingers Holding the hand under the armpit Clean and dry the finger before sticking Do not over 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, or a larger needle. A 21 gauge needle is recommended. The higher the gauge number – the smaller the needle. A 30 gauge needle is much smaller than a 21 gauge needle, and not recommended for INR testing.  

How often should I test?

Medicare guidelines recommend testing not more that once per week. Research has shown that statistically, people on warfarin blood thinners have an 80% chance of a hospital or emergency room visit/stay within a 2 year period. Weekly testing drops this adverse event by 90%. Be sure to talk with your doctor before making changes to any of your medications, which could affect your warfarin dose or monitoring schedule. Also, be sure to tell your doctor about any changes to your general health or diet because certain foods, such as leafy greens, potatoes and some herbal supplements, can affect your body’s response to warfarin.  

When should I contact my doctor or 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?

The lower the INR value the thicker the blood. The higher the value the thinner the blood . Your doctor 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 doctor or health care provider.  

What could affect my INR results?

Certain changes such as illness or an increase in leafy green vegetables, or potatoes in your diet can cause a lower INR test results (thicker blood). Antibiotics, Steroids and inhalers can significantly raise INR results (thins blood). 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 ⦁ Over 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 technologies to generate results. Foods that Lower INR (examples) ⦁ Kale ⦁ Spinach ⦁ Brussels sprouts ⦁ Collards ⦁ Mustard greens ⦁ Chard ⦁ Broccoli ⦁ Asparagus ⦁ Green tea ⦁ Potatoes Foods that Raise INR (examples) ⦁ Alcohol ⦁ Blueberrys ⦁ Cranberrys ⦁ Grapefruit  

Are INR meters results reliable?

The Coagu-Sense meter is the most accurate meter available for home use with a clinical variance of ~2%. The Coagu-Sense INR monitor is capable of INR readings from 0.8 to 8.0. Any values outside this reading range the monitor will give a “NO CLOT DETECTED” error message. If you obtain an INR “NO CLOT DETECTED” error message, please call us to review options. You may want 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. Other 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, steroids and inhalers ⦁ 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.  

Is INR Self-Testing Right For Me?

New England Journal of Medicine Research shows that, compared to standard INR monitoring, patients who self-monitor their warfarin therapy have better therapeutic experiences without an increase in side effects or harmful outcomes. In fact, several studies have shown that individuals who monitor their own INR have slightly less bleeding and clotting complications, and that they are more often in the target INR range, meaning that their anticoagulation therapy is better controlled. INR values obtained with the finger stick home testing meter typically correlate well and are able to be replicated with INR results that are determined from venous blood draws, making them reliable. In fact, recent research indicates that self-testing may produce better outcomes for patients who are eligible to participate.  

Antiphospholipid Antibody Syndrome (APLS or APS)

It is important to note that home INR test meters are unreliable in about one-third of patients who take warfarin and who are also affected by the clotting disorder antiphospholipid antibody syndrome (APLS or APS). In these patients, the meter produces INR readings that are too high, or the instruments can report an error message. If you have APS, your INR levels should be checked via a vein draw in a laboratory setting and compared with a POC reading from a finger stick. Only if both values correlate, may it be acceptable for APS patients to use a POC device. APS patients should discuss their testing options with their healthcare providers.  

Do insurance companies pay for home monitoring devices?

Most insurance plans, including Medicare, cover the cost of home INR testing. Medicaid usually does NOT cover this service. Eligibility for INR self-testing under Medicare and most private insurance plans require that you be diagnosed with one of the acceptable diagnostic codes such as: atrial fibrillation, deep vein thrombosis or pulmonary embolism, or have a mechanical heart valve, or be at increased risk for the development of a dangerous blood clot. In addition, you have to demonstrate that you have been taking warfarin successfully for at least 90 days, be able to perform the test at home on your own or with the assistance of a caregiver, undergo training for the use of the device and demonstrate that you know how to use the device correctly.  

How do I get a Home INR meter?

Patient Self Testing can play a valuable role in your self-testing efforts. We can: ⦁ Verify your insurance or Medicare coverage ⦁ Obtain and coordinate the Order from your doctor or healthcare professional ⦁ Provide the meter and test strips for your INR tests ⦁ Provide training to help improve your self-testing skills ⦁ Help manage your testing results ⦁ Ensure that your test results routinely reach your doctor or healthcare professional. Please Call 805-876-3273 for assistance