Mayo Collaborative Services v. Prometheus Laboratories, Inc.
The Supreme Court unanimously ruled that a company's patents on a blood-test method for adjusting drug doses were invalid, because the patents essentially just described a natural bodily relationship and told doctors to consider it.
The decision sets a stricter standard for patenting diagnostic and medical methods, making clear that adding routine, well-known steps to a discovery about how the body works is not enough to make that discovery patentable.
How it got here: A federal trial court found infringement but invalidated the patents; the Federal Circuit twice upheld them; Mayo asked the Supreme Court to review the case.
The Case in Depth
What happened
Prometheus Laboratories held patents on methods using blood tests to help doctors set safe, effective doses of thiopurine drugs for patients with autoimmune diseases like Crohn's disease. Mayo Clinic had bought Prometheus's tests but in 2004 announced it would sell its own similar test using slightly different metabolite thresholds. Prometheus sued Mayo for patent infringement, and Mayo argued the patents were invalid because they merely described a natural relationship between the body's drug byproducts and drug safety.
The question before the Court
Can a company patent a medical test that just tells doctors to measure a chemical in the blood and consider a natural correlation when adjusting a drug dose?
Why it matters
Biotech and diagnostics companies now face a higher bar when trying to patent tests based on newly discovered biological correlations, since merely instructing doctors to measure something and think about a natural relationship won't qualify. Doctors and hospitals gain more freedom to use similar tests without infringing patents, though some worry the ruling could reduce investment in diagnostic research.
What changes now
This is a final merits decision that resolves the underlying patent-infringement lawsuit by invalidating Prometheus's patents entirely, with no remand needed on the patent-eligibility question. The ruling immediately affects how similar diagnostic-method patents are evaluated nationwide, and companies, patent examiners, and lower courts must apply this stricter standard when deciding whether medical-correlation-based inventions can be patented going forward.
What this does not decide
The Court did not decide whether less conventional or more specific steps added to a natural law might have been enough to make a similar diagnostic method patentable, nor did it address broader policy questions about whether diagnostic-method patents should generally be encouraged or discouraged.
How the Court got there
The legal reasoning, step by step
- The Court applied the rule that laws of nature, natural phenomena, and abstract ideas cannot themselves be patented, but a specific inventive application of such a law can be. A patent claim fails this test if it does little more than state the natural law and add generic instructions to 'apply it.'
- The Court identified the correlation between blood metabolite levels and drug safety or effectiveness as an unpatentable law of nature, since it exists naturally in how the body processes the drug regardless of any human invention.
- Examining the patent's three steps — telling doctors to give the drug, telling them to measure metabolite levels, and telling them what the measurements mean for dosing — the Court found each step, and all three together, amounted to routine, well-known activity already practiced by doctors and scientists in the field, not an inventive application of the correlation.
- Drawing on its precedents in Diehr (where added steps built an inventive rubber-curing process around a formula) and Flook (where added steps were merely conventional and did not save an unpatentable formula), the Court found this case weaker than Diehr and no stronger than Flook.
- The Court also weighed a policy concern it has stressed in past cases: granting a patent that ties up a law of nature too broadly risks blocking future scientific work that would build on that same natural relationship, reinforcing that the claims here crossed that line.
- The Court concluded that because the added steps contributed nothing beyond conventional activity to the natural correlation, the patent claims did not describe a patent-eligible application of the law of nature.
Doctrinal impact
Cases affected by this decision
Distinguishes Diamond v. Diehr (450 U. S. 175)
Found this patent's added steps weaker than Diehr's, which had inventively integrated a formula into a whole process.
Reaffirms Parker v. Flook (437 U. S. 584)
Relied on Flook's rule that adding routine, conventional steps cannot make an unpatentable formula patentable.
Reaffirms Bilski v. Kappos
Reaffirmed that the machine-or-transformation test is only a useful clue, not a definitive test of patent eligibility.
Reaffirms Gottschalk v. Benson (409 U. S. 63)
Relied on Benson's warning against patents that are simply overly broad instructions to apply a formula.