Learn more about Clinical Skills today! Standardize education and management competency among nurses, therapists and other health professionals to ensure knowledge and skills are current and reflect best practices and the latest clinical guidelines.
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#ref4">4
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,4 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.4 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.3 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.6
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.5
Refer to the coagulometers manufacturer’s instructions for use for how to turn the monitor on.
Rationale: To ensure that the coagulometer and test strips are working together correctly, perform a quality control test.
Rationale: Excessive heat or humidity will affect the test strips.
Rationale: If any alcohol remains on the finger, it may cause hemolysis and distorted results.
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.
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.
Do not add more blood to the strip.
Rationale: Test strips are for single use only.
Refer to the manufacturer’s instructions for use for steps to retrieve the stored test results.
World Health Organization (WHO). (2010). WHO guidelines on drawing blood: Best practices in phlebotomy. Retrieved December 3, 2021, from http://whqlibdoc.who.int/publications/2010/9789241599221_eng.pdf (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.
Cookies are used by this site. To decline or learn more, visit our cookies page.