How to Use a PT/INR Test Time Monitor at Home

One of the original hand held PT/INR monitors
One of the original hand held PT/INR monitors (Image: Self)

Home blood testing of prothrombin time (PT) and the related International Normalized Ratio (INR) to monitor oral anti-coagulant therapy has gained greater acceptance in the healthcare and regulatory communities as the testing devices have become easier to use and more accurate. Additionally, in 2008 Medicare expanded coverage of home testing of PT/INR to those prescribed the anti-coagulant warfarin (Coumadin) for treatment of chronic atrial fibrillation or venous thromboembolism whereas only those with mechanical heart valves were covered before. While there are several devices on the market for monitoring PT/INR with each requiring a physician's direction and training, most share the simple steps similar to the use of a glucose monitor for diabetes. So if you are a candidate for monitoring your PT/INR at home, this article describes the general steps that may be involved in the process.

Turn on the PT/INR at home monitoring device and allow it to perform, if any, self-diagnostic tests. Use the monitor on a flat surface at room temperature only.

Remove a test strip for the corresponding monitor from its protective packaging and allow it to warm up for a few minutes if it was kept refrigerated, however, do not use the strip if left out of the packaging for more than the allowable time.

Insert the strip into the PT/INR device as instructed and ensure the device recognizes the strip and that it is not expired by confirming as much on the display. Most monitors will not recognize, accept and/or will provide an error if a strip is either inserted incorrectly or expired.

Acquire a drop of blood from a finger stick using a lancet after swabbing the site with an alcohol pad and drying your hands. This is sometimes the most difficult step in the process; try to prick the finger quickly and forcefully, switching fingers as appropriate.

Apply a sufficient size blood drop where indicated to the strip by applying pressure around the finger stick site. Verify that device is testing the blood sample, usually indicated by the display or audible beeps. Any errors after this point will normally require a new test strip and drop of blood.

Wait for the device to display the PT/INR result and confirm any controls are within specifications; use this time to apply a bandage to the finger prick site. Take any appropriate actions based on the result and your associated physician's instructions for monitoring your anti-coagulant therapy.

Warfarin works by reducing the amounts of active coagulation factors IIa, VIIa, IXa and Xa.
Warfarin works by reducing the amounts of active coagulation factors IIa, VIIa, IXa and Xa.

Tips & Warnings

  • Hang in there! A company is developing a non-invasive device using light shined through the skin to determe PT/INR, meaning no more blood sticks.
  • After the blood is applied, the test should take less than a minute. While the PT is measured in seconds, the INR is the most commonly reported result that is unitless and standardized for diagnosis and reagent variability.
  • This is a general article on the use of at home PT/INR monitors for informational purposes only. It is crucial to follow the device's instruction manual and any additional training provided by your healthcare team.
  • Dispose of your used finger stick supplies as appropriate.

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