The FDA Laboratory Developed Tests regulation marks one of the most significant shifts in U.S. diagnostic oversight in decades. The FDA’s new rule phases in full regulation of LDTs over four years, with no grandfathering. This change elevates the importance of IVD CROs, whose regulatory and clinical expertise will be critical as laboratories adapt to stringent new requirements. The rule represents a major transformation in the U.S. IVD landscape and will reshape how laboratories develop, validate, and maintain LDTs.

Introduction

On September 29, 2023, the FDA released a groundbreaking proposed rule that fundamentally redefines how the agency regulates Laboratory‑Developed Tests (LDTs). This proposal shifts LDTs out of decades of enforcement discretion and brings them fully under the FDA’s medical device framework.

Because LDTs are a subset of in vitro diagnostic products (IVDs), the new rule has sweeping implications for clinical laboratories, manufacturers, and the broader diagnostics industry. Under the FDA Laboratory Developed Tests regulation, LDTs will now be treated like other medical devices—requiring quality systems, medical device reporting, registration, listing, and in many cases, premarket review.

For stakeholders across the IVD sector, this change is significant.

Key Points to Consider as the FDA regulates LDTs

1. Expanded Definition of IVDs
   The FDA proposes to explicitly classify LDTs as IVDs under 21 CFR 809.3.
   This means LDTs will now fall under the same requirements as traditional IVD medical devices.
2. Phased, Four‑Year Implementation
   The FDA will remove enforcement discretion in five stages over a four‑year timeline.
   Each stage introduces new regulatory obligations for laboratories.
3. No Grandfather Clause
   The proposal does not exempt existing LDTs. All LDTs (old and new) must eventually comply.
4. Test Categories Exempt from Enhanced Oversight
   Certain test types, including forensic tests and HLA assays, are proposed for exemption.
5. Public Comment Period
   Stakeholders were invited to submit comments through December 4, 2023.

Background on FDA Regulation for LDTs and IVDs

IVDs have traditionally been subject to rigorous regulatory scrutiny under various heads:

• 510(k) premarket notification or premarket approval (PMA)
• Quality system regulation
• Medical device reporting
• Registration and listing
• Labeling

LDTs, however, historically operated under enforcement discretion, receiving minimal oversight. This approach was based on the assumption that LDTs were low risk and used primarily within single laboratories.

That landscape has changed.

The Evolving Landscape of LDTs

Over the last 50 years, LDTs have become increasingly complex, widely used, and technically sophisticated. This evolution has driven demand for stronger oversight in areas such as:

• Clinical validity
• Analytical performance
• Manufacturing consistency
• Patient safety

The new FDA Laboratory Developed Tests regulation directly responds to these gaps. By redefining LDTs and removing enforcement discretion, the FDA aims to strengthen public health protections.

The Road Ahead: Key Regulatory Impacts

The phased implementation timeline will introduce major compliance requirements:

Medical Device Reporting

The first enforcement area to take effect.

Quality Systems Regulation

Expected three years after publication of the final rule.

Premarket Review

Introduced 3.5 to four years after the final rule, starting with high‑risk LDTs and expanding to moderate-and-low risk tests.

Labs performing LDTs must begin planning now. Clinical and analytical validation, documentation systems, and regulatory processes will all require upgrades.

Alignment With Europe’s IVDR Rollout

The FDA’s new approach mirrors developments in Europe under the In Vitro Diagnostic Regulation (IVDR). The IVDR already applies strict rules to in‑house tests and LDTs, requiring:

• Complete Technical Documentation
• A compliant Quality Management System
• Performance evaluation and validation
• Adherence to Article 5.5 requirements for in‑house devices

çUnder IVDR, an LDT cannot be used if an equivalent CE‑marked test exists. This forces laboratories to justify in‑house development and meet near‑manufacturer‑level standards.

Conclusion: An Industry in Transition

As experts in IVD quality, regulatory, and clinical operations, MDx CRO encourages laboratories and manufacturers to prepare now for the FDA Laboratory Developed Tests regulation. Although legal challenges may influence the timeline, increased oversight is inevitable, and already fully established within Europe under the IVDR.

Stakeholders should submit comments to the FDA by December 4, 2023, and begin strengthening their regulatory systems immediately.