Drafting claims for methods of diagnosing and treating patients can be challenging since they involve the measurement of patent-ineligible subject matter and because these methods are often performed by multiple parties.

But "Test and Treat" claims are particularly desirable when connected to regulatory approval of a drug for use in patients with a positive test result. These claims must be carefully written to capture patent-eligible aspects of the diagnostic method in a manner that ensures that at least one party is held accountable in the event of infringement.


In the United States, multiple parties are typically involved in a patient's diagnosis and subsequent treatment. A hospital or clinic usually does the initial examination and makes the decision to run a test. They may take samples and perform the tests themselves with in-house diagnostic equipment or contract with a third-party diagnostic laboratory facility. When the results are ready, a physician generally interprets them and determines which intervention to apply.

Two problems

When drafting method claims that cover a diagnostic testing method, two problems arise. First, the subject matter will include patent-ineligible elements because the method measures a natural phenomenon. That is especially true if the method merely recites performing the test and making a diagnosis. Second, the divided responsibilities of the laboratory and the hospital might mean that neither party performs all the elements of the method claim, allowing the parties to evade infringement liability.

As articles of manufacture, diagnostic testing products are patent-eligible subject matter. However, under the Mayo standard, the testing methods performed at the diagnostic facility encroach on patent-ineligible subject matter because the diagnostic process unavoidably involves measurement of a naturally occurring phenomenon.1 Subject matter eligibility comes from novel applications of the naturally occurring phenomenon beyond making a diagnosis merely based on the test numbers. This is often just a matter of semantics because subject matter eligibility hinges not on what you claim, but how you claim it.

For example, an improved method of testing cholesterol levels and diagnosing hyperlipidemia would not be patent eligible without a nexus to a significant improvement attributable to the testing device, nor would treating with a statin based on the diagnosis. The steps for detecting cholesterol levels, even if novel, would not be patent eligible under the Mayo standard, nor would making the diagnosis, because it is a measurement of a naturally occurring phenomenon. The method of treatment would probably not be patent eligible because using statins to treat high cholesterol is well known in the art. For the method to be patent eligible, the care provider would need to do more than simply get a cholesterol number and administer the drug known to treat the number. For instance, a feature of the device that produces a more precise measurement could be argued to be patent eligible. Likewise, administering a particularly effective statin based on the test results may be eligible.


The Mayo standard has been sharply criticized for being too limiting to the patentability of novel medical diagnostic technologies.2 Claim drafters might not be able to avoid the restrictions prescribed by Mayo, but there are a few strategies that they should consider. For one, an applicant interested in protecting diagnostic technologies should be made aware of Mayo, so that they understand how a diagnostic method must be disclosed and claimed to cover patent-eligible subject matter. Additionally, article of manufacture claims should be written whenever possible.

It is also good strategy to move forward with diagnostic method claims despite the Mayo standard because it is possible the standard may change soon. In response to wide-spread criticism of Mayo, a bipartisan group of senators drafted a letter to the Commissioner for Patents stating that "action should be taken to reform our eligibility laws" and calling on the USPTO to collect information on patent eligibility jurisprudence.3 In response, the USPTO recently submitted a request for comments over how the current patent eligibility jurisprudence affects the conduct of business in areas including precision medicine, diagnostic methods, and pharmaceutical treatments.4 There is a possibility that the comments could result in recodification of the patent law regarding subject matter eligibility. If patent eligibility laws are revised, a patent-ineligible claim could become eligible over the course of prosecution. Until the law changes, should a diagnostic testing application be restricted between product and diagnostic method claims, the method claims should be elected last.

Who is at fault?

In addition to subject matter eligibility issues, an applicant needs to consider who, if anyone, could be held liable for infringing the claims of a patent that involve diagnostic testing and treatment. When a single party performs all elements of a particular claim, they directly infringe the patent. But when two or more parties collectively perform all elements of a particular claim, one or even both of the parties can be off the hook for liability depending on the circumstances.

In Akamai v. Limelight, the Federal Circuit explained that when multiple parties are involved in "divided infringement," one party's actions can be attributed to another party. However, this only occurs when (1) one entity directs or controls the other party's performance or (2) the actors form a joint enterprise.5

More Solutions

For these reasons, claims relating to diagnostics should be carefully drafted to ensure at least one party is held liable, even if the claimed elements are performed by two parties.

One way to ensure that at least one party is held liable for infringement is by writing the claims such that only one party could directly infringe on the patent. In particular, the claims should be written to cover the patent-eligible work performed by the hospital, clinic, or physician, omitting as much patent-ineligible language directed to work being done by the clinic. For example, a method claim could begin at the step of receiving testing method results from a diagnostic facility. If a method claim includes a step of collecting samples, the applicant should carefully consider how to claim the collection step.

Consideration should be given to drafting a Jepson-type claim format. In a Jepson claim, the preamble identifies the elements of the invention known in the art, with the body of the claim reciting the "portion of the claimed combination which the applicant considers as the new or improved portion.vi" One can modify this format to recite the patent-ineligible subject matter in the preamble and the patent-eligible material in the body of the claim. This would provide an opportunity to argue that all the claim elements are performed by a single party.

Beware the risks

One should bear in mind there are risks inherent in presenting Jepson-type claims because they are subject to narrow interpretation and, in this example, they concede which claim elements are directed to patent-ineligible subject matter and provide a target on which to focus prior art challenges. Such claims are best presented as a fall back position should other claim formats lead to divided infringement.

Contractual relationships

If divided infringement steps cannot be avoided, bear in mind that Akamai provides circumstances where both parties can be held liable. For example, a hospital or clinic may have a contractual relationship with a diagnostic company that may place a lab under the control of a health care network or create a joint enterprise. Under such circumstances the hospital would be held liable because the actions performed by the diagnostic company are attributed to the hospital. Furthermore, if a court finds that the hospital and diagnostic company form a joint enterprise, the applicant may be able to recover from both parties. For this reason, it may still be favorable to also write claims to cover actions taken by both parties.

At one time it was considered inefficient and bad brand strategy for a patent owner to assert a patent against hundreds of humble family physicians for the act of caring for their patients using test results obtained using a patented diagnostic method. With the consolidation of health care into large practice groups that are typically affiliated with a regional hospital network, these considerations are going the way of house calls. If the network includes a lab affiliate, the elements of control or joint enterprise may be present that render the divided infringement actionable under Akamai.

Finally, while one party can be held liable for the actions of another party through active inducement of infringement, this concept would rarely apply to diagnostic claims when multiple parties perform the claim elements. Liability by inducement requires the induced party to directly infringe on all elements of a claim. This is another reason to write method claims, when possible, directed to the actions of a single party.


Obtaining patent protection over diagnostic technologies and methods is therefore challenging, but not always insurmountable. An applicant should be aware of patent eligibility limitations, and should carefully consider who, if anyone, would be held liable when multiple parties perform the elements of a claim.


1. Mayo Collaborative Servs. v. Prometheus Labs., Inc., 566 U.S. 66 (2012).

2. See e.g. Shahrokh Falati, Patent Eligibility of Disease Diagnosis, 21 N.C. J.L. & Tech. 63 (2020).

3. Letter from Senators Thom Tillis, Tom Cotton, Mazie Hirono, and Christopher Coons to Drew Hirshfeld (March 5, 2021).

4. Patent Eligibility Jurisprudence Study, 86 Fed. Reg. 36257 (July 9, 2021).

5. Akamai Techs., Inc. v. Limelight Networks, Inc., 797 F.3d 1020, 1022 (Fed. Cir. 2015).

Originally published 16 August, 2021

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.