What Happened
In 2012, the Supreme Court decided Mayo v. Prometheus, making it much harder to patent diagnostic methods. The case involved a test that measured drug levels in blood to adjust dosages. The Court said the correlation between drug levels and effectiveness was a natural law, and adding conventional detection steps didn't make it patentable.
Why It Matters
Since Mayo, most diagnostic method patents have been invalidated. The problem: tests typically involve discovering a natural correlation (this biomarker indicates that disease) and then applying conventional detection methods. Courts say the correlation is a natural law, and routine detection steps don't add enough to make it patentable.
Some diagnostic patents survive—those with genuinely novel detection techniques, specific technical improvements, or integration with treatment steps. But the bar is high.
This creates a problem for companies investing in diagnostic development. If you can't patent your test, competitors can copy it once you disclose it. Many companies resort to trade secret protection, but that only works if the test can't be reverse-engineered.
What You Should Know
If you're developing diagnostics, think about protection early. Consider claiming specific technical implementations, not just the correlation. Claim the detection apparatus, not just the method. Claim treatment methods that incorporate the diagnosis.
File internationally. Europe, Japan, and China are more permissive about diagnostic patents than the U.S. A global filing strategy can provide protection where the U.S. won't.
Consider whether trade secrets work better. If your test uses proprietary reagents or processes that can't be reverse-engineered, secrecy might provide longer protection than a patent anyway.
Diagnostic innovation is valuable, but U.S. patent law makes it hard to protect. Plan accordingly.