Home INR Monitoring Clinical Outcomes

Improving outcomes for patients on warfarin includes improving patient safety, the quality of warfarin management, and time in target range.

Patient Safety

Patient safety in oral anticoagulation is not limited to reducing or eliminating the risk of bleeding; it includes the prevention of blood clots that often lead to a stroke, heart attack or pulmonary embolism. Adherence to a patient prescription is critical to patient safety. Alere provides a warfarin adherence program for all patients participating in our Home INR Monitoring program. It is one component to improving patient safety.

When patients adhere to their doctor’s instructions, improved clinical outcomes result.

Safety for patients taking warfarin is associated with keeping patients in or very close to their therapeutic target range. Alere takes pride in providing a 74% time in therapeutic range for their weekly patient self-testing population.1

Outcome Improvements

Improving warfarin outcomes includes improving the quality of warfarin management. Over the last 10 years, outcomes for warfarin have improved dramatically. Clinical trials from 2003-2011 have included time in therapeutic range significantly higher than in trials between 1989-1993, resulting in a reduction in stroke rates from 2.09% to 1.66% per year. The improvement in clinical outcomes represents a 20% reduction in stroke within the last ten years vs. the prior ten years.1

Contributing to the improvement in clinical outcomes includes the increased use of patient self-testing. The approval and reimbursement of patient self-testing began in 2002 and expanded to include atrial fibrillation and DVT/PE in 2008. Time in therapeutic range for weekly self-testing has been shown to a achieve 74% in a real-world evaluation.2

High Quality Warfarin Management

Defining the quality needed to manage warfarin to maintain an efficacy and safety advantage over new oral anticoagulants is an area of great interest to clinicians, patients and payers. Recently, the international peer-review journal Expert Opinion on Emerging Drugs evaluated dabigatran, rivaroxaban, and apixaban and determined that warfarin controlled at 65.5% or higher yielded no clinical benefit of switching patients off warfarin.

An additional element of risk includes the traditional poor adherence to chronic medications that do not require routine monitoring. With warfarin, adherence is validated with each INR test result reassuring the prescribing physician that patients are taking their medication as directed. The advantage of new agents over warfarin is the reduced incidence of intracranial hemorrhage (ICH). Studies demonstrating a reduced ICH rate did not find this advantage when warfarin was well controlled.1, 2, 3

The STABLE study (pending publishing) not only demonstrated high quality warfarin management, but did so in a real-world population of over 29,500 patients for two and a half years and sustained the high quality of warfarin control.4


Three independent investigators1, 2, 3 have set the quality of warfarin control from 65.5% to 73% or higher in order for warfarin to be a safer and more efficacious choice for patients than the new agents. The STABLE study found weekly self-testing exceeded all published levels of warfarin control needed to switch patients to a new agent. Self-testing remains a covered service under Medicare and most private insurance plans for indications including atrial fibrillation, DVT/PE, and mechanical heart valve replacement patients.5

Time in Therapeutic Range (TTR)

Time in therapeutic range (TTR) has significant limitations as a sole measure of warfarin patient safety. A patient with an 85% TTR may be at far greater risk than a patient with a TTR of 60%, here’s why:

Patient (100 tests)


% Critical Value

INR’s 1.8 – 3.9



15% (15 tests)

0 tests



3% (3 tests)

37 tests

While Bob appeared to be the safer patient using only TTR as a surrogate measure, his missed INR test results swung to critical value increasing his risk for stroke and bleeding (3.5 fold, 6 fold than if he were in or close to his therapeutic range).1,2 Mary, on the other hand, appeared less controlled by TTR but her out-of-range test results were close to her therapeutic range, resulting in very little if any risk of adverse events.

A 29,529 patient real-world study found weekly patient self-testing experienced a 49% reduction in the incidence of critical value* INR tests   over self-testing patients who tested with more than 7 days between tests.3

 *Critical value: < 1.5 or > 5.0

Time in therapeutic range is limited in its role of evaluating warfarin patient safety. Determining the frequency of extreme values is a more reliable predictor of short and long term patient and practice risk.

Benefits of Home INR Monitoring

The benefits of Home INR Monitoring (also referred to as patient self-testing) go far beyond the convenience of performing the simple fingerstick outside a traditional office or hospital setting. Self-testing is a clinical tool that allows doctors and nurses to increase the testing frequency and reduce critical value test results for patients taking warfarin. Medicare has established a reimbursement code to support a testing frequency ‘up to and including weekly testing’ to meet the pharmacology and pharmacokinetics need of warfarin monitoring.1

Medicare’s reimbursement for up to and including weekly was the result of reviewing 20 independent clinical trials spanning over 30 years of international and U.S. based studies.

Weekly testing empowers patients, removes worry between office visits, and improves patient safety. “The probability that an individual's average INR will be out of range decreases as the number of tests increases. Therefore, the proportion of patients with average INRs out of range may decrease as number of tests increases. All things being equal, increased frequency of testing should lead to a more accurate assessment of TTR.”1

Home INR Monitoring provides clinically relevant INR tests between routine clinician visits, providing a higher level of INR visibility resulting in control and quality of care for your patients. The increase in testing frequency also provides you with additional data points, including allowing you to address INR results that are out-of-range more quickly.2 And since maintaining the proper INR level can be difficult for many people, more frequent testing is recommended for patient safety and it allows you to adjust medication dosage sooner, if needed.

Defining and Reducing Warfarin Risk

Warfarin risk applies to not only to each patient, but also the practice that manages the warfarin patient. For decades the global focus for reducing risk has focused on time patients spend in their therapeutic range. Despite its widespread use, time in therapeutic range (TTR) has great limitations and is not the most reliable measure of warfarin control. Using the incidence of critical value INR results is a more effective marker for warfarin risk.

Critical value results include INR test results, 1.5 or greater than 5.0. At these levels, patients are 3.5 times the risk for thrombosis1 over an in-range result whereas an INR of 5.0 increases a bleeding risk 6 times that of a test result in range.2

A way to reduce the incidence of critical value INR test results is to increase patients’ testing frequency. “More frequent testing also provides the ability to detect any drift in INR stability sooner, rather than later, thus keeping INR within a set range.”2

The largest single study of real-world patients self-testing found a dramatic 49% reduction in critical value risk in patients that tested weekly, this benefit was sustained for the two and half year study period.


Manage your anticoagulation patients at your fingertips.

The web-based Alere CoagClinic® decision support application allows you to keep track of INR results, dosing and more – anytime, anywhere.

Call Alere at 1.866.408.1205 to talk to an associate today!