Study highlights:
• A large study of veterans on blood thinners found weekly home monitoring of clotting speed to be as safe as monthly testing at a clinic.
• Home monitoring might be an alternative for patients whose disabilities or distance from a medical facility make clinic visits difficult.

NEW ORLEANS, La., Nov. 12 — Home monitoring of clotting speed is as safe as clinic monitoring in patients taking warfarin, a common blood thinner, researchers reported at the American Heart Association’s Scientific Sessions 2008. The results of A Prospective Randomized Controlled Trial of the Impact of Home INR testing on Clinical Outcomes: The Home INR Study (THINRS) were presented as a late-breaking clinical trial.

But in the first study designed to determine whether weekly home tests of blood clotting speed are better than monthly tests performed at a clinic, researchers failed to find any superiority for home testing, said Alan K. Jacobson, M.D., study co-chair, staff cardiologist at the Jerry L. Pettis Memorial Veterans Administration (VA) Medical Center and an assistant professor at Loma Linda University School of Medicine, Loma Linda, Calif.

The researchers randomized 2,922 patients to one of the two testing methods and followed them for an average of three years. During that time, 7.9 percent of the home testing participants had the composite endpoint of stroke, major bleeds or death compared to 8.9 percent of the clinically tested patients.

“There was a slight trend toward weekly home monitoring providing a minor improvement over monthly clinic monitoring, but it failed to reach statistical or clinical significance,” Jacobson said. “Once a month at the clinic seems to be just as good as weekly testing at home for most patients.”

Home testing might be the better choice in certain situations such as for patients whose disabilities or distance from a clinic might keep them from appointments, Jacobson said.

The participants in the randomized study were among 3,745 veterans being treated with the anticoagulant warfarin at 28 VA hospitals across the country. The patients all had either an irregular heart beat called atrial fibrillation (AF) or had received a mechanical heart valve — conditions that increase the risk for blood clots that can travel to the brain and cause stroke.

Furthermore, the participants were trained to use the home monitors, which measure how quickly the blood clots, to reduce any effect the training might have on the study results, said David B. Matchar, M.D., co-chair of the trial and director of the Duke Center for Clinical Health Policy Research in Durham, N.C. and Duke-NUS Graduate Medical School Program in Health Services Research, Singapore.

Patients with AF or mechanical heart valves take warfarin to slow the speed at which their blood clots. However, the safe range for clotting speed is narrow. If the drug doesn’t thin the blood enough, the patient could develop a life-threatening blood clot. If the drug works too well, it could lead to hemorrhage such as a bleeding ulcer or a hemorrhagic stroke. As a result, most patients on warfarin need to have a test tube of blood drawn at a clinic each month to be sure their anticoagulation is in range.

The patients were deemed able and willing to perform home monitoring. The monitors used just about four drops of blood.

In addition to the unpleasantness of drawing blood and the constant risk that patients may decide to skip appointments — particularly when blood draws are involved — many veterans must travel long distances to reach a clinic.

“What we did show was that home testing is every bit as effective as regular clinic monitoring,” said Jacobson, whose clinic has been using at-home testing since 1995 with a special computerized system to keep tabs on many of its patients. “For patients where access is a problem either because of disability or distance, this potentially has a huge impact.”

“THINRS was far and away the largest and most ambitious trial of home anticoagulation monitoring. The bad news is that we didn’t show home monitoring to be superior. The good news is that patients using home monitoring did every bit as well as the patients in the clinic.”

Other co-authors are: Rowena Dolor, M.D.; Robert G. Edson, M.A.; and Lauren Uyeda, M.S., M.B.A. Individual author disclosures can be found on the abstract.

The study was funded by the U.S. Department of Veterans Affairs (Clinical Science Research and Development, Cooperative Studies Program, project number CSP 481).

Statements and conclusions of study authors that are presented at American Heart Association scientific meetings are solely those of the study authors and do not necessarily reflect association policy or position. The association makes no representation or warranty as to their accuracy or reliability. The association receives funding primarily from individuals; foundations and corporations (including pharmaceutical, device manufacturers and other companies) also make donations and fund specific association programs and events. The association has strict policies to prevent these relationships from influencing the science content. Revenues from pharmaceutical and device corporations are available at http://www.americanheart.org/corporatefunding. 

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NR08-1163 (LBCT-SS-08/Jacobson)
 

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