Prothrombin Time/International Normalized Ratio Testing (Home Health Care) - CE

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Prothrombin Time/International Normalized Ratio Testing (Home Health Care) - CE


If the patient is receiving warfarin, obtain the blood specimen before the patient receives the daily dose of warfarin. The daily dose may be increased, decreased, or kept the same depending on the PT test results for that day.undefined#ref3">3


Oral anticoagulation therapy with vitamin K antagonists (e.g., warfarin) is prescribed both prophylactically and therapeutically for patients at risk of venous thromboembolism, such as those with prosthetic heart valves, atrial fibrillation, or venous thrombosis. The purpose of monitoring the PT/INR is to determine the clotting tendency of the blood.

Good therapeutic control via regular monitoring of PT/INR to analyze the clotting tendency of blood is imperative to minimize adverse events. Oral anticoagulant therapy requires regular and frequent monitoring to ensure that the INR is within the therapeutic range and to reduce the risk of hemorrhage and blood clots. Point-of-care INR testing eliminates delays in waiting for the result of PT measurements to be processed by a laboratory and the subsequent delay in adjustment of anticoagulation dosing.

In the home setting, monitoring of the INR can be done with a portable blood coagulometer using a finger-stick blood sample applied to a test strip (which may come in cartridge or cassette form, depending upon the manufacturer). The therapeutic range is typically between 2 and 3 seconds,3 depending on the reason the patient is on anticoagulation therapy. An INR above 5 seconds is considered a critical value and should be reported to the practitioner immediately.3 Excessively milking the finger-stick site, not allowing alcohol to dry before performing the finger-stick, delaying the application of the blood sample to the test strip, or applying an inadequate amount of blood to the test strip can cause distorted INR results.2 Optimized management of oral anticoagulation therapy improves the quality of treatment. Medication dosage changes are based on the INR results to reduce the risk of complications; therefore, all PT/INR results must be reported to the practitioner.1

Research results are mixed regarding the effect of dietary intake of vitamin K on the coagulation response. Dietary modifications may not be necessary when initiating a regimen of vitamin K antagonists.5

Quality control is an important part of PT/INR testing to ensure that the coagulometer is functioning correctly. The manufacturer of the coagulometer provides control solution with a known INR value to test functioning, not the accuracy of the monitor. Some devices also have internal quality control, eliminating the need for an external quality control solution.4


See Supplies tab at the top of the page.


  • Provide developmentally and culturally appropriate education based on the desire for knowledge, readiness to learn, and overall neurologic and psychosocial state.
  • Teach the patient, family, and caregivers proper storage for test strips.
  • Teach the patient, family, and caregivers to correctly perform the procedure.
  • Teach the patient, family, and caregivers the importance of a wallet card or medical alert bracelet or necklace to inform emergency health care providers that the patient is taking oral anticoagulants.
  • Instruct the patient, family, and caregivers to contact the practitioner before taking any new prescription or over-the-counter medication.
  • Teach the patient, family, and caregivers to distinguish between minor and major bleeding, and teach them emergency measures for major bleeding.
  • Teach the patient, family, and caregivers the signs and symptoms of a blood clot and provide instructions on when to seek additional care.
  • Discuss any dietary concerns with the patient, family, and caregivers.
  • Instruct the patient to use an electric razor for shaving instead of a razor with a blade.
  • Encourage questions and answer them as they arise.


  1. Perform hand hygiene before patient contact. Don appropriate personal protective equipment (PPE) based on the patient’s need for isolation precautions or risk of exposure to bodily fluids.
  2. Introduce yourself to the patient, family, and caregivers.
  3. Verify the correct patient using two identifiers.
  4. Explain the procedure to the patient, family, and caregivers and ensure that the patient agrees to treatment.
  5. Verify the practitioner’s order and assess the patient for pain.
  6. Prepare an area in a clean, convenient location and assemble the necessary supplies.
  7. Place the blood coagulometer on a stationary, even surface.
  8. Check the expiration date of new test strips.
    1. If the strip has been refrigerated, allow the strip to reach room temperature before opening the pouch.
    2. The strip must be used within a specified time after opening the pouch. Refer to the manufacturer’s instructions for use.
  9. Turn the coagulometer on. When prompted by the coagulometer, insert the test strip into the test strip guide on the monitor.
    Refer to the coagulometers manufacturer’s instructions for use for how to turn the monitor on.
  10. Perform a quality control test per the manufacturer’s instructions for use.
    Rationale: To ensure that the coagulometer and test strips are working together correctly, perform a quality control test.
  11. If the quality control test fails, attempt to correct the problem with these steps:
    1. Verify that the test strips were stored properly.
      Rationale: Excessive heat or humidity will affect the test strips.
    2. Verify that the strip code matches the code on the monitor display.
    3. Ensure that the test strip was not contaminated during testing.
  12. Perform hand hygiene and don gloves.
  13. Locate a puncture site on the tip of the finger near the top to either side of the center. Choose a site that is free from scars, lesions, and calluses.
  14. Clean the puncture site with an alcohol wipe or with 70% isopropyl alcohol and a clean gauze pad. Allow the site to dry completely.
    Rationale: If any alcohol remains on the finger, it may cause hemolysis and distorted results.
  15. Puncture the fingertip using a lancet or lancing device.
  16. Apply light continuous pressure until a large drop of blood forms.
  17. Do not squeeze or milk the finger-stick site excessively because doing so may release interstitial fluid into the blood sample, potentially causing distorted results.
  18. When prompted by the coagulometer, immediately apply the blood sample onto the test strip. With some coagulometers, a capillary tube may be used to collect and apply the blood sample.
    Rationale: The blood sample will begin to clot if it is not applied immediately, which will result in inaccurate results.
    Do not apply the blood sample before the monitor is ready; an error will occur.
  19. Ensure that the coagulometer beeps and counts down as it performs the test. If the monitor does not beep or count down, an insufficient blood sample was used.
    Do not add more blood to the strip.
  20. If necessary, remove the test strip and retest using a new test strip.
    Rationale: Test strips are for single use only.
  21. Hold a gauze pad to the puncture site until the bleeding stops.
  22. Retrieve the test results, which are automatically stored in the coagulometer’s memory, along with the date and time of the test.
    Refer to the manufacturer’s instructions for use for steps to retrieve the stored test results.
  23. Assess pain, treat if necessary, and reassess.
  24. Discard or store supplies, place the lancet in a puncture-proof container, and clean the outside of the monitor per the manufacturer’s instructions for use.
  25. Remove PPE and perform hand hygiene.
  26. Report the PT/INR results to the practitioner.
  27. Document the procedure in the patient’s record.


  • Appropriate blood sample is obtained for testing.
  • Puncture site clots appropriately.
  • Test strip works correctly.
  • Test results are obtained.


  • Excessive bleeding.
  • Excessive bruising.
  • Internal bleeding.
  • Blood clot.


  • Test results
  • Collection date and time of blood sample
  • Assessment findings
  • Unexpected outcomes and related interventions
  • Current or changed medication dosage per practitioner’s order
  • Practitioner communication
  • Education
  • Patient’s progress toward goals
  • Assessment of pain, treatment if necessary, and reassessment


  • Many older adults take multiple medications, some of which may interfere with anticoagulation therapy. The patient’s medications should be reviewed and the practitioner notified of any potential interactions.
  • Older adults at risk for falls should be educated about fall prevention, because increased bleeding or hematoma may occur after trauma while taking anticoagulants.


  1. da Silva Saraiva, S. and others. (2016). Home management of INR in the public health system: Feasibility of self-management of oral anticoagulation and long-term performance of individual POC devices in determining INR. Journal of Thrombosis and Thrombolysis, 42(1), 146-153. doi:10.1007/s11239-016-1335-6 (classic reference)* (Level VI)
  2. Larsen, T. (2017). Nurses’ instruction of patients in the use of INR-monitors for self-management of cardio-vascular conditions: Missed instructional opportunities. Patient Education and Counseling, 100(4), 673-681. doi:10.1016/j.pec.2016.10.001 (Level VI)
  3. Pagana, K.D., Pagana, T.J., Pagana, T.N. (2022). Chapter 2: Blood studies. In Mosby’s manual of diagnostic and laboratory tests (7th ed., pp. 11-497). St. Louis: Elsevier.
  4. Sharma, P. and others. (2015). The clinical effectiveness and cost-effectiveness of point-of-care tests (CoaguChek system, INRatio2 PT/INR monitor and ProTime Microcoagulation system) for the self-monitoring of the coagulation status of people receiving long-term vitamin K antagonist therapy, compared with standard UK practice: Systematic review and economic evaluation. Health Technology Assessment, 19(48), 1-172. doi:10.3310/hta19480 (classic reference)* (Level I)
  5. Violi, F. and others. (2016). Interaction between dietary vitamin K intake and anticoagulation by vitamin K antagonists: Is it really true? A systematic review. Medicine (Baltimore), 95(10), Art. No.: e2895. doi:10.1097/MD.0000000000002895 Retrieved November 4, 2022, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4998867/ (classic reference)* (Level I)


World Health Organization (WHO). (2010). WHO guidelines on drawing blood: Best practices in phlebotomy. Retrieved November 4, 2022, from (classic reference)* (Level VII)

*In these skills, a “classic” reference is a widely cited, standard work of established excellence that significantly affects current practice and may also represent the foundational research for practice.

Elsevier Skills Levels of Evidence

  • Level I - Systematic review of all relevant randomized controlled trials
  • Level II - At least one well-designed randomized controlled trial
  • Level III - Well-designed controlled trials without randomization
  • Level IV - Well-designed case-controlled or cohort studies
  • Level V - Descriptive or qualitative studies
  • Level VI - Single descriptive or qualitative study
  • Level VII - Authority opinion or expert committee reports

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