Laboratory Developed Test (LDT)
A laboratory developed test (LDT) is an in vitro diagnostic that is designed, manufactured and used within a single laboratory certified under CLIA for high-complexity testing.
What is a laboratory developed test?
The FDA has historically described an LDT as an in vitro diagnostic test designed, manufactured and used within a single CLIA-certified laboratory that meets the requirements for high-complexity testing. It is generally offered as a laboratory service rather than distributed as a test kit. Genetic panels, oncology assays and specialty biomarker tests are common examples, but whether a particular arrangement fits the concept depends on how the test is made, transferred and used.
What did the FDA's 2024 LDT rule do?
The May 2024 final rule amended the regulatory definition of in vitro diagnostic products to state expressly that they are devices even when the manufacturer is a laboratory. The FDA also announced a staged phaseout of its general enforcement-discretion approach for many LDTs, which would have brought increasing application of medical-device reporting, registration and listing, quality-system and premarket-review requirements over several years.
What is the status after the 2025 court decision?
On 31 March 2025, a federal district court vacated the final rule. The government did not appeal. On 19 September 2025, the FDA issued another final rule reverting the IVD definition to its text before the 2024 amendment. Those are the precise legal events; describing the court as categorically deciding that every LDT is outside the FD&C Act goes beyond the FDA's current summary. As of August 2026, laboratories must still meet applicable CLIA requirements, while the FDA's historical LDT policies and any product-specific device issues require careful review.
Why does the LDT boundary matter to IVD manufacturers?
A distributed test kit and a test performed as a service by one laboratory have different operational and regulatory profiles. Specimen-collection devices, instruments, software, companion-diagnostic claims and components supplied to laboratories may raise their own FDA questions in the United States. A manufacturer should map each entity, product and transfer rather than assume that association with a CLIA laboratory makes the complete offering an LDT.
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