The LDT Rule, Vacated: What Changed for Diagnostic Diligence

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FDA's May 6, 2024 final rule would have phased laboratory-developed tests (LDTs) into medical device oversight over four years, ending in May 2028. It never got that far. On March 31, 2025, a federal district court vacated the rule in a challenge brought by the American Clinical Laboratory Association and the Association for Molecular Pathology, and FDA did not appeal. On September 19, 2025, FDA issued a final rule restoring the regulation's pre-2024 text.

This article was first published while the rule's status was still being described as settled. It has been rewritten to reflect the court decision and FDA's rescission.

What the 2024 Rule Would Have Required

The rule amended the definition of in vitro diagnostic products in 21 CFR 809.3 to include tests made by laboratories. It set out a staged end to FDA's general enforcement discretion for LDTs, starting with medical device reporting in May 2025 and ending with premarket review requirements in 2027 and 2028.

Where LDT Oversight Sits Now

With the rule vacated and the regulation text restored, LDTs remain under the Clinical Laboratory Improvement Amendments (CLIA), administered by CMS. CLIA governs laboratory quality; it does not review a test's clinical validity the way FDA premarket review would. Test kits sold to other laboratories remain in vitro diagnostic devices under FDA's rules, and some states add their own requirements: New York, for example, reviews laboratory tests offered to its residents.

What Still Matters in Diligence

The questions have moved from compliance timelines to fit. Is each revenue-generating test an LDT, an FDA-cleared or approved kit, or both? Do the test's claims, marketing and distribution fit LDT status, or do they look like a kit sold to other laboratories? Does any test depend on a state approval, such as New York's? What clinical validity and utility evidence would a payer see, given that CLIA does not supply it? And how exposed is the business if Congress or FDA revisits LDT oversight?

The 2024 rule is no longer in effect. For a diagnostics company, the record worth reading is how each test is regulated today, and whether its claims, distribution and payer evidence fit that status.