Inventors of methods of medical testing have had a rough time since the Supreme Court decided Mayo Collaborative Services v. Prometheus Labs. Inc. In the Mayo case, the Court considered whether a method of determining whether a patient is receiving the proper dosage of thioguanine drugs is eligible for patenting, when the method involved measuring the concentration of a specific metabolite of thioguanine in the patient’s blood. The inventor had determined the safe range of dosages was not based not on the dosage itself (which varied a great deal from person to person), but depended on the concentration of the metabolite. The Court concluded that the patent merely claimed a relationship between metabolite concentration, safety, and efficacy of the drug, which without more is not an invention.
Since Mayo was decided, courts have invalidated numerous medical testing patents as subject matter that is not eligible for patenting (See, e.g., Cleveland Clinic Foundation v. True Health Diagnostics, LLC, Genetic Tech. Ltd. v. Merial LLC, Ariosa Diagnostics, Inc. v. Sequenom, Inc., SmartGene, Inc. v Advanced Biological Labs., and PerkinElmer Inc. v Intema Ltd.).
This makes the recent decision by a panel of the U.S. Court of Appeals for the Federal Circuit in Exergen Corp. v. Kas USA, Inc. something of a unicorn. Exergen patented a forehead thermometer that functions by measuring the radiative output of the skin at least three times per second, identifying a peak temperature that indicates that the thermometer has passed over an artery, and executing an algorithm based on the peak temperature and the ambient air temperature to calculate the patient’s core body temperature. Some of the asserted patent claims included the limitation that the artery is the temporal artery (located in the side of the forehead). The Exergen thermometer has the advantage over prior art thermometers of measuring a patient’s core temperature noninvasively, a benefit every parent can appreciate. Several companies, including Kaz, offered similar forehead thermometers, and Exergen filed several infringement suits in the U.S. District Court for the District of Massachusetts, which were consolidated only for claim construction purposes. Among other defenses, Kaz alleged that all of Exergen’s asserted patent claims were invalid as non-eligible subject matter for patenting under the Mayo decision.
The Trial Court Decision
At trial the judge ruled from the bench that the asserted claims were eligible subject matter as a matter of law. The jury found that Kaz infringed the patents and awarded damages. On appeal Kaz argued that the trial court had impermissibly decided the question of patent eligibility without sending the relevant factual questions to the jury, and, in the alternative, that Exergen’s claims were not patent eligible as a matter of law.
The Appellate Decision
Among the claims at issue were both method claims and apparatus claims. Claim 24 of the ‘685 was considered by the appellate court as typical of the apparatus claims, and reads as follows:
A body temperature detector comprising:
a radiation detector; and
electronics that measure radiation from at least three readings per second of the radiation detector as a target skin surface over an artery is viewed, the artery having a relatively constant blood flow, and that process the measured radiation to provide a body temperature approximation, distinct from skin surface temperature, based on detected radiation.
Note that the electronics are defined mainly by their function. Claim 14 of the ‘938 was considered by the appellate court as typical of the method claims, and reads as follows:
- A method of detecting human body temperature comprising
making at least three radiation readings per second while moving a radiation detector to scan across a region of skin over an artery to electronically determine a body temperature approximation, distinct from skin surface temperature.
The court applied the general test in Alice for patent eligibility (readers of this blog can review the Alice test here). The court found that the claims fell under the categories of subject matter Congress intended should be patented, as expressed in 35 U.S.C. § 101, as “machines” and “processes.” The court went on to conclude the claims were “directed to” one of the judge-made exceptions to the statutory categories, specifically the “law of nature” that physiologic core temperature is a function of skin temperature above an artery and ambient temperature. Based on these two conclusions, a claim would not be eligible for patenting unless as a whole it encompasses “substantially more” than natural law itself.
Kaz argued that the claims were not substantially more than the simple recognition of the relationship between skin temperature above an artery, ambient temperature, and core temperature. In Kaz’s view, the remaining parts of the claims were “conventional, well understood” elements. In support of this argument, Kaz cited the undisputed fact that the use of infrared radiation measurements of the skin to detect internal injuries was known before Exergen’s invention, and such measurements were made at a rate exceeding three readings per second.
The appellate court disagreed with Kaz’s argument and affirmed the district court’s finding that the claims were directed to substantially more than the natural law. Regarding the older method of detecting internal injury, the court pointed out that “Something is not well-understood, routine, and conventional merely because it is disclosed in a prior art reference… This case is not like either Mayo or Ariosa, where well-known, existing methods were used to determine the existence of a natural phenomenon.” In other words, the inventors in Mayo and Ariosa identified the relationship between an analyte and a condition, and claimed measuring the analyte by only well-understood, routine, and conventional methods (in Mayo the broadest claims were not specific to the measurement methods at all). Exergen’s claims included an unconventional method of determining core body temperature, which was novel independent of the recognition of the specific relationship between the temperature of the skin above an artery and the patient’s core body temperature. Although body radiation sensors were known, none had been configured to convert skin temperature to core temperature; although methods of measuring skin temperature with a radiation sensor were known, none had specifically measured skin temperature above and artery and converted it to core temperature.
How Does Exergen Fit with Current Case Law?
Comparing Exergen to Mayo, in Mayo the measurement of the metabolite was claimed generally, not by any specific method, conventional or otherwise. Measuring the metabolite was well-known and conventional. The claims in Mayo thus involved only a well-known and conventional step, in combination with reaching a diagnosis. Although the criteria used for the diagnosis were not previously known, others had tried to use the metabolite concentration to diagnose the same condition using different criteria. In contrast, Exergen claimed steps that had never been performed before — measuring skin temperature over an artery by radiometry, in addition to the more abstract steps of calculating core temperature.
The distinctions between this case and Ariosa are more subtle, and the two cases might seem inconsistent. The patent in Ariosa did claim steps that had never been performed before; namely, it recited amplifying paternal DNA in a maternal whole blood sample. The court focused on the fact that the paternal DNA was claimed to be measured by conventional methods (polymerase chain reaction), so that nothing substantial was added to the concept of measuring the paternal DNA itself. In Exergen, the court defined the measured property as body core temperature, and found that it was neither routine nor conventional to measure body core temperature as claimed. However, if the court had considered ultra-arterial skin temperature to be the measured property, instead of core temperature, it might have concluded that the claimed steps were conventional and well-understood ways of measuring it.
This distinction can serve as guidance going forward: Defining exactly what is being measured can be determinative of the Alice analysis of medical tests. Those seeking to patent or defend medical testing claims could benefit from defining the measured property narrowly. Alternatively, those seeking to invalidate medical testing patents should seek to define the measured property broadly as something that has been measured before in the same way. For example, does the invention measure core temperature by measuring ultra-arterial skin temperature by radiometry, or does it measure skin temperature by radiometry? The latter steps were known in the prior art, while the former were not.