Oral Anticoagulation Patient Self-Testing: Consensus Guidelines For Practical Implementation - Part 1

Challenges of Managing Patients on Warfarin Therapy

Oral anticoagulation therapy with warfarin is effective in reducing the risk of thromboembolism in patients with hereditary or acquired thrombophilia, heart valve replacement, atrial fibrillation (AF), and other conditions (Heneghan 2006) (P=.001). The goals of oral anticoagulant therapy are to prevent thromboembolism and to minimize the risk of bleeding complications by achieving and maintaining the international normalized ratio (INR) within an appropriate target range. However, warfarin’s narrow therapeutic range, variable biological effects, and potential for drug and food interactions, including fluctuations in patient dietary intake of vitamin K-containing foods, present challenges to reaching these goals (Ansell 2004). Because of these factors, regular INR

monitoring is required to determine dose adjustments that may be necessary to maintain the INR in the target range. The mean plasma half-life of warfarin is approximately 40 hours, and the mean terminal half-life of a single dose is approximately 1 week (warfarin PI 2007).  U.S. Food and Drug Administration-approved labeling of warfarin now includes a black box warning regarding

the risks of major or fatal bleeding. Risk factors for bleeding include high intensity of anticoagulation (INR>4.0), age 65 or older, highly variable INRs, history of gastrointestinal (GI) bleeding, hypertension, cerebrovascular disease, serious heart disease, anemia, malignancy, trauma, renal insufficiency, concomitant drugs, and a prolonged duration of warfarin therapy. Those at high risk of bleeding may benefit from more frequent INR monitoring, careful dose adjustment to the desired INR, and a shorter duration of therapy (warfarin PI 2007). 

In the United States, approximately 75 percent of patients taking warfarin are managed individually by a physician or other practitioner (CMS 2008), with periodic office visits that include INR testing performed either by centralized laboratory methods or with pointof- care (POC) INR devices in the office. In this setting, referred to as usual care, patients are typically evaluated by the practitioner once every 4–6 weeks, any INR-based dose adjustments are then prescribed, and patients remain on that dose until the next office visit. Alternatively, monitoring by anticoagulation clinics provides a standardized system of patient management, and this type of care has been associated with improved outcomes relative to the usual care model (Ansell 2005).

Patient Self-Testing

Patient self-testing (PST) may consist of weekly, as indicated, INR testing with a home INR device in addition to regular office visits with the health care practitioner. Each week, the patient communicates the INR to the practitioner, who then instructs the patient about any dose adjustments that may be needed.  PST is not a stand-alone management method; ideally, it should be combined with periodic visits to an nticoagulation

clinic or a health care practitioner’s office on a predetermined schedule for clinical assessment, patient education, and periodic parallel testing of the patient’s INR device. Patient self-management (PSM) occurs in addition to all the components of a weekly self-testing program, and includes teaching the patient to follow a practitioner-prescribed, dose-adjustment algorithm based on weekly INR values. In addition to the extensive body of evidence supporting the efficacy, safety, and improved quality of life associated with PST (Ansell 2005, Sawicki 1989, Heneghan 2006), additional factors (discussed later in this monograph) support its incorporation into the U.S. care model for patients who require oral anticoagulation. As the general patient population has become better informed about health care, patients desire a more active role in the management of their health. PST, like home blood-glucose monitoring by patients with diabetes, is a simple and practical method that enables more frequent testing, and has been demonstrated to improve INR control and significantly reduce the risk of bleeding and thrombotic complications.

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