A federal court struck down the FDA’s final rule to regulate laboratory‑developed tests (LDTs), marking a major judicial check on agency rulemaking in 2025. The decision halted a broad effort by the agency to bring many LDTs under FDA premarket and compliance oversight. The ruling has immediate consequences for clinical diagnostics companies, hospital labs and biotech firms that supply tests: regulatory uncertainty returns, and stakeholders anticipate litigation, legislative responses or revised agency rulemaking. The case underscores the legal and political complexity of governing diagnostic tests and will shape diagnostic commercialization and compliance strategies into 2026.