It is worthwhile to look at how the Prometheus ruling applied the machine-or-transformation test to the patented diagnostic technique for determining an appropriate dose for thiopurine. The court found the claims satisfied its test by constituting a transformation. It stated: "The transformation is of the human body following administration of a drug and the various chemical and physical changes of the drug's metabolites that enable their concentrations to be determined." Measuring the level of the metabolites "is also transformative" because the levels "cannot be determined by mere inspection" and require "some form of manipulation, such as ... high-pressure liquid chromatography." The court also stated that one "further requirement" must be met: The transformation requirement cannot be satisfied by "merely insignificant extra-solution activity." The court found the transformation required by Prometheus's patent was central to the claims because they "are part of treatment regimes for various diseases using thiopurine drugs." Whether anything other than a mere visual inspection of the patient would fail to qualify under the machine-or-transformation test remains to be seen.

One curious aspect of the Prometheus decision is that all of the steps in the claims, up until the final required mental step of "determining" to adjust the dose, appear to be in the prior category and are thus valid, according to the court's opinion. Prior to the issuance of the Prometheus patent, according to the decision, doctors administered thiopurine to patients at various doses and knew of techniques to measure the metabolites, even if they did not yet know how to correlate them with dosing. Now, those same doctors for all practical purposes cannot measure thiopurine metabolite levels without risking infringement—even if they never adjust the dose—because unless they are ill-informed of the literature, it may be impossible for them not to draw the mental conclusion that a different dose would be appropriate.

The challenge for companies moving forward is the number of hurdles that still must be breached to ensure certainty in fixing the patent eligibility of critical new technologies like diagnostics. These include three sizable ifs: if the Federal Circuit reaches the same conclusion in Prometheus upon remand from the Supreme Court in light of Bilski, which is possible because the machine-or-transformation test is still a "useful tool;" if the Supreme Court's three dissenters in a previous case, Labcorp v Metabolite Laboratories, never persuade a majority of the Supreme Court to adopt their views; and if subsequent Federal Circuit decisions follow the Prometheus decision. Only then will companies be able to take comfort in knowing that patentable subject matter is applied broadly to diagnostic techniques and be able to determine in the future which diagnostic methods are most likely to be eligible for patent protection.

Daniel Reisner