Patenting Diagnostic Methods in the US

The patentability of diagnostic inventions has long been a source of frustration for innovators seeking protection in the United States. While many jurisdictions permit patent protection for diagnostic methods provided they are appropriately claimed, the position in the US has been considerably more challenging over the past decade.

Recent developments at the United States Patent and Trademark Office (USPTO) have led some practitioners to wonder whether the USPTO might be softening its stance. However, applicants should be cautious about assuming that the difficulties have disappeared.

The US approach

Under US practice, patents are obtainable for “any new and useful process, machine, manufacture or composition of matter, or any new and useful improvement thereof” (35 U.S.C. 101). However, the courts have long recognised certain judicial exceptions from patentable subject matter. In the context of diagnostics, the relevant judicial exceptions are laws of nature and natural phenomena.

USPTO examiners assess patent eligibility (i.e. patentability) using a framework developed by the USPTO from Supreme Court case law. A key question is whether a claim is "directed to" a judicial exception and, if so, whether the claim includes additional features that amount to “significantly more” than the judicial exception itself. If the claim is considered to be directed to a judicial exception without including “significantly more”, then the claim is deemed patent ineligible. In practice, many applicants and practitioners have viewed this framework as being applied particularly restrictively to diagnostic technologies. Claims involving naturally occurring biomarkers, disease correlations or genetic associations have often struggled to satisfy the patent eligibility requirements, creating substantial uncertainty for innovators in the diagnostics sector.

For diagnostics, the most influential decision remains Mayo Collaborative Services v. Prometheus Laboratories, Inc., 566 U.S. 66 (2012). The patent at issue concerned a method of optimising the dosage of a thiopurine drug by measuring metabolite levels and determining whether the dosage should be adjusted. The Supreme Court concluded that the claims were effectively directed to a natural relationship (i.e. law of nature) and merely added conventional steps such as administering a drug and measuring metabolites. The claims were therefore held to be patent ineligible. 

Signs of change?

However, recent developments have prompted renewed discussion about the future treatment of diagnostic claims.

In August 2025, the USPTO issued the so-called Kim Memo, reminding examiners that eligibility rejections should only be made where there is a clear basis for concluding that a claim is more likely than not ineligible. It emphasised that claims should be considered as a whole, that uncertainty alone is insufficient to justify a rejection, and that technological improvements should be properly recognised. Importantly for diagnostic inventions, the guidance also reminded examiners that they must distinguish between claims which are directed to a judicial exception (e.g. a law of nature or natural phenomenon) and claims which involve a judicial exception. It also stresses the importance of considering whether any natural relationship has been integrated into a practical application.

The new Director of the USPTO has also drawn attention to the patent eligibility of diagnostic claims. During his first official patent signing ceremony, one of the patents granted (US Patent No. 12,419,201) was directed to detecting human pro-epiregulin using a specific antibody. In particular, the patent contains claims directed to contacting a biological sample with the antibody and detecting binding of the antibody in the sample. Although the claim refers to a novel antibody, there are no other steps of the method recited, such that there does not appear to be any features which amount to “significantly more” than the natural biological interaction between the antibody and its target (i.e. a law of nature/natural phenomenon).

Some practitioners have interpreted the Kim Memo and the prominence of US 12,419,201 in the USPTO Director’s signing ceremony as a potentially positive signal for the diagnostics sector. Others, however, are less optimistic. In particular, the Kim Memo seems to be mostly aimed at the high-tech space, and US biotechnology practitioners report mixed experiences, with outcomes often depending heavily on the individual examiner and the specific facts of the case, and continued significant difficulties for diagnostic methods.

Practical drafting strategies

Despite the difficulties, there are strategies for improving the prospects of obtaining patent protection in the US for a diagnostic method. It is advisable to consider each of these when drafting a patent application, and to include as many as possible in the patent specification, thereby providing multiple fall-back positions in the event that an examiner does consider the claim to be patent ineligible: 

1. Claim detection rather than diagnosis – a claim which recites a method of detecting a biomarker, without mentioning the patient population or a diagnostic step, may be less at risk of a rejection on the grounds of being a mental process and/or directed to a law of nature/natural phenomenon. In this context, a diagnostic step would include a step of comparing a measured value to a reference value, and not only a step of determining a diagnosis. The comparison step may be considered to relate to a mental process.
2. Include a step of treating the subject in the diagnostic method claim. US practitioners have advised that a combination of detection and treatment steps seems to result in less scrutiny of the claim than if the claim recited only detection/diagnosis steps. In addition, it appears that the more specific the treatment step(s), the greater the chance of avoiding an objection of patent ineligibility. In particular, the treatment step may help show that the law of nature/natural phenomenon has been integrated into a practical application. However, applicants should note that claims reciting both diagnosis and treatment steps can be harder to enforce, because a given party may not be carrying out both the diagnosis and the treatment – it may be different parties carrying out these two steps.
3. Limit the diagnostic method to being used in a patient subgroup, for example, subjects suspected of having a particular disease or condition. Although there is no clear authority that such limitations improve eligibility by themselves, they may strengthen an argument that the claimed method if directed to a specific practical application rather than a mere observation of a natural correlation. 
4. Include novel physical processing methods or unconventional aspects of the diagnostic method in the claim. This may provide a feature which is “significantly more” than the judicial exception itself. Such novel processing methods or unconventional aspects may include any features of the preparation of the sample or of the diagnostic method itself which are novel or unconventional.
5. Include in the patent specification explanations of any technical improvements provided by the diagnostic method. USPTO guidance indicates that improvements in technology should be recognised during eligibility analysis, and applicants should therefore explain how the invention improves, for example, assay performance, sensitivity, specificity, workflow efficiency or other technical characteristics. Where possible, experimental evidence supporting these technical advantages should also be included in the specification.

It is also relevant that the delay between filing a patent application and substantive examination of the patent application means that applications filed today may be examined under a different policy environment from that which exists today. A pending application may therefore have significant strategic value even if the legal position continues to evolve.

Conclusion

The US represents one of the world's largest healthcare and diagnostics markets, and the USPTO’s approach to the patent eligibility of diagnostic methods may be worrying for diagnostics companies. While there appears to be some shift in the position of the USPTO on the patent eligibility of diagnostic methods, the message should not be that the US eligibility problem has been solved - rather, it is that recent developments provide at least some grounds for cautious optimism, and that careful patent drafting can significantly improve the chances of obtaining valuable protection.

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