Background
Metabolite Laboratories, Inc. held U.S. Patent 4,940,658, which covered a method for detecting deficiencies of cobalamin (Vitamin B12) and folate in humans. The patent claimed a two-step process: first, assaying a body fluid sample to measure the level of total homocysteine (an amino acid); second, “correlating” elevated homocysteine levels with a deficiency in cobalamin or folate. Researchers had discovered that elevated homocysteine is a reliable biomarker for these vitamin deficiencies.
Metabolite licensed its technology to Competitive Technologies, which in turn licensed it to LabCorp. LabCorp initially used the patented test as licensed but later switched to a third-party assay method — a different way of measuring homocysteine — without paying royalties to Metabolite. Metabolite sued for breach of contract and patent infringement, arguing that even though LabCorp used a different assay, it still infringed the patent by correlating the homocysteine test results with vitamin deficiency (the second step of the claimed method), which was necessarily performed by the physicians who ordered and interpreted the tests.
The district court entered judgment for Metabolite after trial, awarding $4.7 million in damages and entering a permanent injunction against LabCorp.
The Court’s Holding
The Federal Circuit affirmed the judgment. On the infringement question, the court agreed that claim 13 (the correlating step) was infringed by LabCorp’s conduct through indirect infringement: LabCorp provided the homocysteine test results to physicians who necessarily performed the correlation step by reading and interpreting the results. The court construed the “correlating” step as simply relating total homocysteine levels to cobalamin or folate deficiency — an unavoidable mental step performed by any physician who ordered and interpreted such a test. LabCorp was thus liable for induced infringement of the physicians’ direct infringement.
The Federal Circuit did not reach the question of whether the claimed method — essentially, the act of observing an established natural correlation — was even patentable subject matter under 35 U.S.C. § 101. The Supreme Court granted certiorari to address that question, with three Justices (Breyer, Stevens, and Souter) writing to say they believed the patent claimed a natural phenomenon and should be held invalid. In 2006, the Supreme Court dismissed the case as improvidently granted without reaching the merits, leaving the Federal Circuit’s judgment in place.
Key Takeaways
- A method patent’s “correlating” step can be performed by a physician through the act of reading and interpreting a test result, making the test provider liable for inducing infringement.
- Indirect infringement (inducement) requires that the induced party (the physician) directly infringe the patent, even if the infringing act is a mental step.
- The case raised but did not resolve whether a patent can validly claim a method consisting of observing a naturally occurring biological correlation — a question that would resurface dramatically in Mayo Collaborative Services v. Prometheus Laboratories (2012).
- Even after abandoning a licensed test, a party may still infringe if it provides services that cause others to perform the remaining steps of the claimed method.
- The Supreme Court’s dismissal left intact a precedent that the patent bar viewed as deeply problematic, fueling continuing controversy over the patentability of natural phenomena and diagnostic methods.
Why It Matters
Metabolite v. LabCorp was an early and important skirmish in the battle over the patentability of natural phenomena and diagnostic methods — a battle that culminated a decade later in Mayo Collaborative Services v. Prometheus Laboratories (2012), in which the Supreme Court unanimously held that claims directed to natural laws cannot be patented merely by adding conventional application steps. Justice Breyer’s dissent from the Metabolite dismissal laid out the reasoning that would eventually carry the day in Mayo.
For the clinical laboratory industry, the case created real uncertainty: if the act of observing a correlation in test results is itself an infringing act, clinicians and laboratories face patent liability for basic diagnostic practice. This anxiety about diagnostic method patents drove significant interest in clearer limits on patentable subject matter, ultimately contributing to both the Mayo decision and the AMP v. Myriad Genetics (2013) ruling that isolated human genes are not patentable. Metabolite v. LabCorp is thus a foundational case in understanding the trajectory of § 101 patent eligibility law.