Point-of-Care Testing of the International Normalized Ratio (INR) for Patients Taking Warfarin or Other Vitamin K Antagonists

CADTH has undertaken an optimal use project to assess the clinical and economic impact of point-of-care (POC) testing of the international normalized ratio (INR) for patients taking warfarin or other vitamin K antagonists.

Patients with atrial fibrillation, prosthetic heart valves, or venous thromboembolism may be prescribed oral anticoagulation therapy (OAT) with warfarin or other vitamin K antagonists to prevent blood clots. When taking these drugs, patients must be monitored to ensure that they are getting the right amount of the medication and are not at risk for bleeding or blood clots. The standard method for monitoring the drug therapy is laboratory testing of blood obtained by venipuncture to measure the INR. POC testing is another way of monitoring the INR. POC testing is defined as testing at or near where a patient is located.

There are three main ways in which POC INR testing can be implemented:

• Patient self-management (PSM), in which the patient self-tests the INR using a POC device, and also self-adjusts the dose of the anticoagulant medication based on the results using a predetermined algorithm or protocol
• Patient self-testing (PST), in which the patient self-tests the INR using a POC device and a clinician adjusts the dose of anticoagulant medication based on the results
• Clinic-based POC INR testing, in which POC testing is performed in a clinical setting such as a physician’s office or anticoagulation clinic.

CADTH conducted a review of the clinical evidence and performed a health economic analysis to compare POC INR testing with standard INR laboratory testing. Feedback from interested stakeholders was sought at key stages of the project. An expert advisory committee comprised of experts from across Canada, HTERP (the Health Technology Expert Review Panel), was established to help CADTH provide guidance on this and other optimal use projects.

The objective of this project is to determine:

• In which clinical settings POC INR could be considered
• If there is a preferred POC INR test.

The project aims to provide health professionals, policy-makers, and patients with the evidence-based resources they need to make informed decisions.

Key Messages

CADTH’s work on this project resulted in the following key messages:

For Health Care Providers and Your Patients Taking Warfarin:

• Point-of-care (POC) INR testing is accurate.
• Offer patients, if they are willing and able, the option to test their own INRs and make dose adjustments to their medication. Provide them with education and support.
• If patients are not willing or able to manage their own dose adjustments, self-testing of INR with dose adjustments by a health professional may be an option, but only if there are significant barriers to patients having their INR regularly tested in a lab.
• POC INR testing in a clinic can be more costly than lab testing; however, consider the context of your practice site before implementing.

For Health Care Decision-Makers and Health Care Providers:

• Point-of-care (POC) INR testing with any currently available POC INR device is an accurate alternative to lab INR testing.
• Patient self-management (POC INR testing + dose adjustment) is the most cost-effective option, when feasible.
• Patient self-testing with health care provider dose adjustment may be an option when lab INR testing is difficult.
• Clinic-based POC INR testing requires careful consideration of context and costs.

Tools

The Canadian Agency for Drugs and Technologies in Health (CADTH) developed the following tools to help transition our recommendations from paper into practice. To make these tools relevant to different audiences, CADTH can tailor specific tools to individual needs and settings. Contact us if you would like our assistance in tailoring any of these tools to meet your unique needs as a health care provider, policy-maker, or consumer.

POC INR Costing Tool ― a tool for decision-makers who are considering the implementation of POC INR technology. The tool helps estimate the total costs of patient self-management, patient self-testing, or clinic-based POC INR testing by allowing users to enter setting-specific information regarding case load, practice patterns, and costs.

Point-of-Care INR Testing ― a newsletter article summarizing CADTH's work on POC INR testing for patients taking warfarin or other vitamin K antagonists. This article originally appeared in the August 2014 edition of Hospital News, Canada's health care newspaper since 1987.

Point-of-Care INR Testing Compared with Lab INR Testing: What Does the Evidence Say? Tool ― an at-a-glance tool that outlines the different ways POC INR testing can be used to monitor INR compared with standard laboratory testing.

Stakeholder feedback was considered at specific stages of this project.

Reports

Our project on Point-of-Care Testing of the International Normalized Ratio for Patients Taking Warfarin or Other Vitamin K Antagonists resulted in the following reports: 

Final Reports

• Project Protocol
• Recommendations Report
• Science Report