LDTs are a type of diagnostic test that are designed, manufactured, and analyzed within the same laboratory. These tests are sometimes referred to as “in-house” or “home brew” tests as well. You may have encountered an LDT at a university’s medical center or a major lab like Labcorp or Quest, if the test you received was designed, developed, and analyzed within a single lab, but as the patient, it’s difficult to know.

Examples of LDTs include ARUP Laboratories’ Vitamin E test, Labcorp’s beta amyloid test for Alzheimer’s Disease, and Accu Reference Medical Lab’s test for free cortisol.

The Clinical Laboratory Improvement Amendments (CLIA) program regulates laboratory testing and is run by the Centers for Medicare and Medicaid Services (CMS). To obtain CLIA certification, laboratories are required to conduct quality control, maintain proper records and equipment operations, and employ qualified personnel. CLIA ensures the tests measure what they say they are measuring (i.e., analytical validity), but maintaining this oversight is a small part of the CLIA program. FDA regulation would ensure that the test is useful and relevant in the condition it is meant to diagnose (i.e., clinical validity), in addition to more in-depth analysis of analytical validity. Additionally, CLIA’s oversight applies after tests are in use, whereas FDA regulation would ensure that LDTs are safe and effective before they reach consumers.

When FDA first developed its medical device regulations, LDTs were used in small, local patient populations for uncommon tests and thus deemed low enough risk for FDA to exercise enforcement discretion. This means that FDA decided to not regulate LDTs at the time due to the low risk profile of the tests but reserved the option to exercise oversight if new risks arise in the future. Once the increased prevalence of LDTs came to the attention of FDA, the agency has put out policies and guidances to try and address the safety and effectiveness of LDTs and their components.

It depends! The over-the-counter COVID-19 tests you purchase at a pharmacy are direct-to-consumer tests, and this category of tests are FDA-regulated. The type of COVID-19 tests done at a lab or healthcare provider’s office may be LDTs, and thus not FDA-regulated. During the pandemic, FDA identified major issues with some COVID-19 tests, highlighting the need for regulatory oversight for laboratory-developed tests.

For questions about specific test results, speak with your healthcare provider.

• A lab test you get might be an LDT depending on where you get it.
• Most routine labs are straightforward and likely reliable, even if they are LDTs. But you have no way of knowing whether a particular LDT may have problems.
• Patients, and often providers, may not know if the test they have done is an LDT.
• If LDTs are falsely positive or falsely negative, they can lead to unnecessary medical treatments or delays in receiving care.