Understanding Labcorp’s laboratory developed tests (LDT) and in vitro diagnostics (IVD)

In 2025, Labcorp launched the pTau-217/Beta Amyloid 42 Ratio assay, marking a significant milestone in Alzheimer's disease evaluation. This blood test aids in the identification of amyloid-related pathology and was validated at Labcorp’s Monogram Biosciences. It was initially introduced as a laboratory developed test (LDT). A product version of the test was later granted clearance by the FDA as an in vitro diagnostic (IVD) device and it was re-launched by Labcorp using the FDA-cleared kit.

This designation made the pTau-217/Beta Amyloid 42 Ratio assay the first blood test for Alzheimer’s disease to receive FDA clearance with commercial availability as an IVD. But what does it mean that a test is authorized by the FDA for marketing either through 510(k) clearance or PMA approval and how is that different from an LDT? Here’s what to know.

What is a laboratory developed test (LDT)?
LDTs are diagnostic test services developed, validated and performed by trained professionals within a single laboratory entity. These tests are often developed as a response to market need when no IVD options are available. This allows performing laboratories like Monogram Biosciences to tailor tests to meet specific clinical needs.

“LDTs are instrumental in advancing care and innovation in areas like Alzheimer’s disease,” says Dr. Chris Petropoulos, Vice President of Research and Development at Monogram Biosciences. “Labcorp’s LDTs undergo rigorous scientific validation and quality control processes to ensure their accuracy and reproducibility.”

In addition to stringent scientific protocols and validation processes, LDTs are regulated under a statutory and regulatory framework—the Clinical Laboratory Improvement Amendments Act (CLIA). This combined framework ensures the analytical validity and reproducibility of laboratory testing, including the training and qualifications of the skilled professionals who perform, supervise and interpret those tests.

 “Labcorp's LDTs are developed and maintained under strict quality management systems that often exceed regulatory requirements,” says Dr. Marcia Eisenberg, chief scientific officer at Labcorp.

What is an in vitro diagnostic (IVD) device?
IVDs can take many forms, such as reagents, instruments and lab systems. In the case of laboratory tests, IVDs are commercially distributed diagnostic products that are required to undergo FDA premarket review of analytical and clinical performance and receive authorization for marketing as devices.

“This regulatory process ensures that IVDs meet specific benchmarks before becoming commercially available to CLIA-accredited laboratories,” says Dr. Eisenberg.

Common examples of IVDs include general wellness screening or routine tests like cholesterol or thyroid function. Because IVDs can be marketed to multiple organizations, including large reference laboratories like Labcorp, community hospital labs and academic centers, they require the additional step of FDA oversight and clearance. This extra step helps to standardize tests that are run at multiple laboratory entities across the country.

What's the difference between LDTs and IVDs?
While both LDTs and IVDs aim to diagnose and monitor health conditions, they differ in their routes to market, regulatory review and operational framework. LDTs are services developed and performed within a single laboratory entity, which allows for greater customization but also means they are not marketed or sold to other labs outside the developing laboratory entity. This was the case when Labcorp launched the pTau-217/Beta Amyloid 42 Ratio assay as an LDT.

“At Labcorp and Monogram, LDTs allow us the flexibility to address unmet clinical needs like the delivery of novel tests for Alzheimer’s disease,” says Dr. Petropoulos.

In contrast, IVDs undergo FDA review through a formal premarket submission process resulting in clearance or approval that permits distribution across multiple clinical laboratory entities. So LDTs are unique to one laboratory entity, while IVDs are products standardized and typically available at more than one laboratory entity. Viewing it this way, while they are characterized by important differences for regulatory purposes, LDTs and IVDs both play an important role in diagnostics and can provide accurate and reliable results.

LDTs vs IVDs:  Common misperceptions

• Coverage and reimbursement: Both LDTs and IVDs require efforts to secure coverage and reimbursement from Medicare and commercial insurance plans. Providers should not assume that FDA authorization for marketing or lack thereof impacts coverage in any way—it often does not, because payers evaluate coverage under a different standard than the standard used by FDA. It's important to review the specific policies and recommendations of each insurance provider to confirm that the tests they use are covered and considered medically necessary.
• Clinical practice guidelines: Inclusion in clinical practice guidelines is based on the test's demonstrated clinical utility and impact on patient care and outcomes, not just its regulatory status as an LDT or IVD. Providers should review practice guidelines to understand the evidence that has been generated to support the use of these tests in patient management.
• Analytical performance: The sensitivity, specificity and reproducibility of laboratory analysis is not predicated on its regulatory status as an LDT or IVD. The rigorous scientific validation and quality control processes for both LDTs and IVDs help establish that their performance meets the highest analytical standards.

What’s next for blood biomarkers in Alzheimer’s neurodegenerative conditions?
As innovations continue to reshape the landscape of medical testing, our commitment to thorough validation and quality control means that every test we offer meets the highest standards for clinical use.

“Our launch of the pTau-217/Beta Amyloid 42 Ratio assay—first as an LDT and later as an FDA-cleared IVD—reflects our commitment to scientific excellence and patient-focused innovation,” says Dr. Petropoulos. “This powerful new blood test has helped redefine how Alzheimer’s disease can be evaluated, offering providers a powerful tool to detect pathology earlier and more accurately.”

Building on that foundation, we are dedicated to expanding access to novel diagnostic tools in Alzheimer’s disease and other neurodegenerative conditions to help providers evaluate, diagnose and monitor disease earlier and with greater clarity, and personalize care for every patient. “Our commitment to addressing the unmet needs in neurodegenerative disease is a priority for us,” says Dr. Eisenberg. “Monogram’s work exemplifies the precision and depth of scientific inquiry that Labcorp brings to every diagnostic innovation.”

“We’re entering a transformative era in neurodegenerative diagnostics,” says Dr. Eisenberg. “With every test, we’re delivering tools that bring greater clarity to complex conditions and answers to the patients and families affected by them. By harnessing the strengths of both LDTs and IVDs, we’re advancing the science of dementia care. We’re bringing better tests, clearer answers and more personalized management options to patients and their providers.”

Next steps: When using LDTs and IVDs, providers should:

• Stay informed: Regularly review updates from regulatory bodies, insurance providers, and professional organizations
• Collaborate: Work closely with laboratory directors and clinical pathologists to understand the strengths and limitations of available tests
• Evaluate evidence: Assess the clinical utility of tests through evidence-based practices and patient outcomes

Explore more of our innovations in neurological testing and join us in advancing the science of dementia care.