WASHINGTON - The Mayo Clinic will arrive at the U.S. Supreme Court this week hoping to resolve a centuries-old argument -- can patent protection be applied to a medical or scientific idea?

The point of contention for Mayo is a diagnostic test that allows doctors to measure how individuals absorb a particular type of medicine and use the results to immediately adjust dosages so they are most effective. A California medical laboratory bought the rights to the concept and successfully filed for a patent. The company claimed patent infringement in a lawsuit when Mayo tried to introduce a similar version of the test.

For Mayo, a medical research icon, the court's ruling could redefine ownership of scientific and technological concepts, affecting everything from the delivery of patient care by hospitals to the way medical researchers make discoveries to the development of computer software.

"What is an abstract idea?" said Jim Bessen, a lecturer at Boston University's School of Law who specializes in economic innovation. "This has been an issue since the 18th century when people started asking whether you could patent a concept rather than a process."

Prometheus Laboratories of San Diego bought the rights to a drug protocol from researchers in Montreal. The protocol uses a blood test and a unique set of chemical standards to quickly determine the most effective dose of a drug called thiopurines to treat gastrointestinal disorders. Prometheus received two patents on the test, which it claimed took the guesswork out of constantly adjusting doses to make sure they treat disorders without poisoning patients.

Mayo used the Prometheus test for a while, but in 2004 announced plans to market a similar blood test at a lower cost that applied different standards to determine the optimum dose. At that time, Prometheus sued Mayo for patent infringement.

Mayo countered that Prometheus was trying to patent a natural process and common medical measurements in such a way that it will undermine patient treatment and stifle other important medical discoveries.

A federal appeals court ruled that the Prometheus system can be patented. The Supreme Court will hear arguments Wednesday. A decision will not be issued for several months.

Officials at Mayo and Prometheus declined interview requests ahead of the Supreme Court argument. Patent lawyers and scholars say the outcome matters to patients.

"You don't want to inhibit doctors from treating patients optimally," said Tom Cotter, a University of Minnesota law professor and patent rules specialist.

Supporting briefs for both Mayo's and Prometheus' viewpoints have poured into the Supreme Court from dozens of the biggest names in medicine, science and software in anticipation that the court may break new legal ground in an intellectual property debate that dates back more than 200 years.

"Medical-process patents involving pharmaceuticals ... are the products of human ingenuity, and cannot be found in nature," the powerful Pharmaceutical Research and Manufacturers Association argued in favor of Prometheus.

National medical giants, including the American Hospital Association, the American Medical Association and the Association of American Medical Colleges, filed briefs in support of Mayo. The groups assert that "health care will be undermined if conventional medical applications of scientific observations of naturally occurring bodily processes can be patented."

Like Mayo, they believe that doctors will not be able to offer the best care to patients and researchers will be discouraged from advancing treatments for fear of being sued. Mayo explained its position in legal filings this way: "The tasks doctors and researchers have always performed in this fast-moving field -- test blood and think freely about what results mean -- can now only be performed by paying Prometheus a fee."

That is simply not the case, the American Intellectual Property Law Association insists. The association argues that the law has always protected "medical practitioners" from patent infringement claims.

What Mayo is doing, Prometheus and its supporters argue, is trying to make money through one of its for-profit businesses by trading on a patented diagnostic process owned by Prometheus.

"The assertion that they're trying to patent thought is a misinterpretation of what the claim covers," said Eric Guttag, a long-time patent lawyer affiliated with the Association of University Technology Managers, which also filed a brief in support of Prometheus. "This [case] is about a drug dosage calibration method.

"The assertion by Mayo that Prometheus is trying to stifle medical research is absolute nonsense."

Jim Spencer • 202-408-2752