A woman with Crohn's disease, which causes severe intestinal problems, takes immunosuppressant drugs to manage her condition. Her doctor would like to measure her metabolite levels to see how she's reacting to it. The situation seems straightforward, except that her physician is not allowed to run the check himself—the testing method legally belongs to someone else.

A legal battle surrounding this scenario has pitted Prometheus Laboratories, which patented the test, against the Mayo Clinic, which believes the test is simply an observation of natural processes, and thus nonpatentable.

Notably, the test equipment that measures the metabolite levels isn't patented. What's patented is a range of numbers: 250 pmol to 400 pmol per 100,000,000 red blood cells. If a patient's metabolite levels fall within this range, the drugs—in this case, thiopurine immunosuppressants—are working.

As a patented invention, the test using these numbers costs $270 per test, a price tag that makes it unavailable to some. “As a clinician, I can live without the tests,” says Richard Gearry, a gastroenterologist at Christchurch Hospital in New Zealand, “but life is much easier with them.” The same goes for the patients.

However, doctors have been giving these drugs and measuring their corresponding metabolite levels in patients since the 1970s, says Joe Calaiano, legal counsel at the Mayo Clinic. “Prometheus did not invent the test,” he says. “They just assigned reference numbers to it... according to them, you're not allowed to think about these numbers [without their permission].”

Yet Prometheus was the one to combine the steps of administering the drug, running the test and running their calibration—a process that improves upon previous methods.

“Under traditional methods, to determine whether you are dosing a patient correctly could take months,” says Rick Bress, who represents Prometheus in the case. “Prometheus patent... allows you to determine the correct dosage right from the get-go.”

In 2004, the Mayo Clinic decided to do the testing in house rather than sending samples off to Prometheus—they already had all of the necessary equipment to do so and went about it using a wider efficacy range.

Prometheus sued for patent infringement, and this past September, more than five years later, the US Federal Circuit Court ruled in their favor, stating that the Prometheus test met the requirements of patentability (see 'Machine or transformation test' put to the test itself, on page 1241). The Mayo Clinic isn't giving up—they are appealing their loss to the Supreme Court, and have filed amicus briefs with the American Medical Association.