For years, the Food and Drug Administration has maintained that it has jurisdiction over laboratory-developed tests (“LDTs”) – those in vitro tests developed, validated and used for in-house pathology and diagnostic purposes – as medical devices. Yet the Agency has, with some few exceptions (e.g., IVDMIAs), exercised enforcement discretion, reasoning that most LDTs were simple, well-characterized, and reliant upon various FDA-regulated individual components. As LDTs have become increasingly complex and the laboratory setting increasingly large-scale, FDA has begun rethinking its regulatory approach.