The recent US Supreme Court decision in Mayo Collaborative Services v. Prometheus Laboratories, Inc., No. 10-1150 raises possible challenges for companies attempting to obtain patent protection for diagnostic methods in the US.

The patent claim at issue in Prometheus recited a first step of administering a drug to a patient, a second step of measuring the concentration of a particular metabolite of the drug in the patient’s blood, and a third step of recognizing that a metabolite concentration above a specified threshold indicates a need to decrease the amount of drug subsequently administered, whereas a metabolite concentration below a specified threshold indicates a need to increase the amount of drug subsequently administered. Administering the drug and determining its metabolite concentrations in blood were well known in the prior art. Unknown was the proper metabolite concentration range. What the inventors had discovered was an optimal metabolite concentration range that a doctor could target by adjusting the dosage of the drug.

Although the US Patent Act extends patent protection to “any new and useful process”, established jurisprudence has long held that this provision precludes the patenting of laws of nature, natural phenomena, and abstract ideas. The Court in Prometheus characterized the relation between the metabolite concentration in the blood and the likelihood of the drug dosage being too low or too high as a natural law because this relation exists apart from any human action.

The Court then determined the discrete issue to be whether the patent claims “add enough to their statements of the correlations to allow the processes they describe to be patent-eligible processes that apply natural laws”. The Court held that they did not. The Court found that the steps of administering the drug and measuring the metabolite concentration were “well understood, routine, conventional activity…not sufficient to transform unpatentable natural correlations into patentable applications of those regularities”.

There are concerns that the Court has inappropriately expanded the scope of patent ineligible “natural laws”. The optimal concentration range of a specific metabolite for therapeutic efficacy of a specific drug is arguably distinguishable from the examples of natural laws given by the Court such as e=mc2 and the law of gravity. Since most if not all diagnostic inventions are essentially a discovery of a natural correlation between a biomarker and a medical condition, if these natural correlations cannot form the basis for a patent claim then it is unclear how any diagnostic method claim could still be patent-eligible. There are also concerns that the Court appears to have conflated the threshold issue of patent eligibility with subsequent patentability issues of novelty and non-obviousness by requiring under the patent eligibility analysis an application of the natural law that is beyond “well understood, routine, conventional activity”.

Those seeking US patent protection for diagnostic methods should carefully consider the implications of Prometheus in their claiming strategy. For example claims reciting the discovered correlation could additionally recite specific assay steps, specific reagents and/or specific devices, or improvements thereto, tailored to exploit that correlation and go beyond well understood, routine, conventional activity.