The impact of patient self-testing of prothrombin time for managing anticoagulation: rationale and design of VA Cooperative Study #481--the Home INR Study (THINRS)

Abstract

Background: Anticoagulation (AC) with warfarin reduces the risk of thromboembolism (TE) in a variety of applications, yet despite compelling evidence of the value and importance of high quality AC, warfarin remains underused, and dosing is often suboptimal. Approaches to improve AC quality include (1) an AC service (ACS), which allows the physician to delegate day-to-day details of AC management to another provider dedicated to AC care, and (2) incorporating into the treatment plan patient self-testing (PST) under which, after completing a training program, patients perform their own blood testing (typically, using a finger-stick blood analyzer), have dosage adjustments guided by a standard protocol, and forward test results, dosing and other information to the provider. Studies have suggested that PST can improve the quality of AC and perhaps lower TE and bleed rates. The purpose of Department of Veterans Affairs (VA) Cooperative Studies Program (CSP) #481, "The Home INR Study" (THINRS) is to compare AC management with frequent PST using a home monitoring device to high quality AC management (HQACM) implemented by an ACS with conventional monitoring of prothrombin time by international normalized ratio (INR) on major health outcomes. PST in THINRS involves use of an INR monitoring device that is FDA approved for home use.

Study design: Sites are VA Medical Centers where the ACS has an active roster of more than 400 patients. THINRS includes patients with atrial fibrillation (AF) and/or mechanical heart valve (MHV) expected to be anticoagulated indefinitely. THINRS has two parts. In Part 1, candidates for PST are evaluated for 2 to 4 weeks for their ability to use home monitoring devices. In Part 2, individuals capable of performing PST are randomized to (1) HQACM with testing every 4 weeks and as indicated for out of range values, medication/clinical changes, or (2) PST with testing every week and as indicated for out of range values, medication/clinical changes. The primary outcome measure is event rates, defined as the percent of patients who have a stroke, major bleed, or die. Secondary outcomes include total time in range (TTR), other events (myocardial infarction (MI), non-stroke TE, minor bleeds), competence and compliance with PST, satisfaction with AC, AC associated quality of life (QOL), and cost-effectiveness. To assess the effect of PST frequency on TTR and other outcomes, at selected sites patients randomized to perform PST are assigned one of three test frequencies (weekly, twice weekly, or once every four weeks).