As a general rule, a patent applicant should strive to obtain the broadest possible patent coverage during patent prosecution.  The broadest possible patent coverage has sometimes included open-ended ranges, for example, “at least 10 ppm by weight” or “greater than 3 mA.”  While open-ended ranges are sometimes warranted, the patent applicant should be aware that patent claims that recite open-ended ranges are under heavy scrutiny before the USPTO and in the federal courts.

In order for any patent claim to be valid, the claim must be “enabled.”[1]  For a patent claim to be enabled, the corresponding patent specification “must  teach those skilled in the art how to make and use the full scope of the claimed invention without ‘undue experimentation.’”[2]  For patent claims that include variable ranges, the courts have interpreted the patent statute as requiring the entire range to be enabled in order to satisfy the legal requirement.[3]  A recent decision has further clarified the interpretation by invalidating a patent claim reciting an open ended range that exceeded the state of the art as of the filing date.[4]

The unanimous panel decision will have rippling effects across all technology fields, particularly in the chemical arts.  Patent claims in the chemical arts routinely include ranges of values drawn to one or more variables (e.g., concentrations, molecular weights, flow rates, temperatures, etc.).  When defining these ranges, it is usually wise for the patent applicant to begin with a reasonably broad but bounded range and gradually narrow the range via dependent claims until the “sweet spot” is claimed in the narrowest range.

While the USPTO will give the patent claim its broadest reasonable interpretation,[5] the aforementioned rules related to variable ranges operate to narrow the interpretation. Under the current state of U.S. patent law, there is no benefit to a patent applicant over-reaching beyond a reasonable and operable variable range in a patent claim because the entire range must be enabled by the corresponding specification.  Over-reaching on a variable range in a patent claim can lead to invalidity of each patent claim that relies on the over-reached variable range, and consequently without legal recourse against infringing competitors.