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Originally published March, 1998

IVD Technology News

Blood-thinning monitors go home

Patients who suffer from cardiac and vascular disease are often treated with a daily regimen of blood-thinning drugs. To be effective, however, the amount of anticoagulant in the bloodstream must be maintained at the proper level. Too little drug can allow unwanted clotting, which can lead to stroke; too much can result in nosebleeds and more serious hemorrhaging.

For patients, achieving this balance usually means frequent, costly, and inconvenient visits to a clinic where the blood's ability to clot can be closely monitored. But with recently approved self-testing monitors, manufacturers are hoping to put anticoagulant drug management into patients' hands—and homes.

The Boehringer Mannheim Coaguchek monitor received FDA approval for prescription home use in April 1997. Photo Courtesy Boehringer Mannheim

Currently, only two coagulation monitors have received FDA approval for home use: the Coaguchek (Boehringer Mannheim Corp., Indianapolis), and the Protime (International Technidyne Corp., Edison, NJ). Both machines are intended for use by patients who are receiving the blood-thinning drug warfarin. The downside of warfarin is that it can interact with alcohol, over-the-counter drugs, and some foods. This creates a definite need for patients to constantly monitor their dosage.

Manufacturers claim that their new generation of point-of-care (POC) monitors can deliver prothrombin times (PTs), PT ratios, and international normal ratios (INRs) with speed and ease. Equally important, several pilot studies have found that home-use monitors can give PT values comparable to those of standard analyzers used in clinical laboratories (Bernardo A, Herz Kreislauf, 27(2):71—75, 1995; VandenBesselaar AMHP, Blood Coagul Fibrinolysis, 6(8):726—732, 1995).

Bob Gosselin, a senior specialist in hemostasis at the UC Davis Medical Center, has done extensive work in the field of PT monitoring. He concurs that POC devices are cost-effective and clinically advantageous, but notes that they also have some limitations. His major concern is sample integrity. "Since the operation of these devices is based on clot detection, poor sample acquisition will bias the result." Because the very act of drawing blood can cause platelet activation and blood clotting, consumer education and training are key.

To ensure proper use of its Coaguchek, Boehringer Mannheim requires patients to take a two-hour training course and also offers a toll-free support line. The training is important because FDA requires that Coaguchek users run two quality control tests for each run of the machine. Running QC samples ensures the validity of the results, but it is another step that the patient must be trained to perform. International Technidyne has taken a different approach, maintaining a staff of about 100 clinical trainers who teach physicians and their staff to educate patients.

Not many experts would disagree with the concept of home monitoring, notes Nancy Fabbrini, supervisor of the hemostasis lab at the Hines Veterans Affairs Hospital (Hines, IL) and coauthor of a paper comparing assessment methods for anticoagulant levels. "You can see that POC home monitoring would probably be good for patients, but it isn't like checking glucose levels."

For most practitioners, the advantages of having patients monitor their own warfarin levels far outweigh the risk of biased results. "One has to recognize that many of the benefits aren't related to accuracy," says Jack Ansell, MD, professor of medicine at Boston University. "Most patients take their prothrombin times more frequently" when they use the home device.

Ansell, who has worked as a consultant for Boehringer Mannheim, believes that more-frequent monitoring constitutes a clear advantage that needs to be taken into account. This view is supported by a European study of patients with heart valve replacements that concluded that self-management of oral anticoagulation therapy constitutes a significant service improvement compared to conventional care (Hasenkam JM, Thromb Res, 85(1):77—82, 1997).

Even so, some manufacturers are taking a more cautious approach toward the universal application of POC anticoagulant monitors. "My personal view is that only about 10—20% of people will be suitable candidates to use the new home-model monitors correctly," observes Mike Riddle, vice president for sales and marketing at Cardiovascular Diagnostics, Inc. (Raleigh, NC), a company that produces instruments to monitor coagulation and the dissolution of drugs.

In the end, it may not be PTs and INRs that decide whether anticoagulant monitors are suitable for home use. The Coaguchek currently lists at $1295, with single-use test strips selling for $6 each. The Protime's price tag is even heftier at $2000 and $10 per test packet. A Boehringer Mannheim representative says that some consumers have been reimbursed for their machines, but approval is on a case-by-case basis.

Ultimately, the policies of health-care payers may decide the fate of these POC devices. Without reimbursement coverage, home PT monitors may never leave the showroom floor.—G.W.