In Vitro Diagnostic Design: What are LDT and IVD?

Medical professionals usually rely on various tools to diagnose conditions and guide treatment decisions. The most commonly used is in vitro diagnostics (IVD) technology. Patients may receive or decline medical services based on diagnostic test results, so ensuring the reliability of the tests is crucial. These tests are regulated by medical device regulatory agencies in various countries, so manufacturers must undergo a series of strict testing, validation, and clinical trials to confirm the accuracy and usability of the test in diagnosing specific diseases before they can be marketed. However, the FDA exempts some tests developed by medical laboratories themselves, known as laboratory-developed tests (LDTs). LDTs are only used within the medical laboratory and cannot be sold as diagnostic reagents to any other medical laboratory, hospital or individual.

What is commercial IVD and how is it regulated?

IVD refers to the process of obtaining clinical diagnostic information on diseases through the detection and verification of human samples (blood, body fluids, tissues, etc.) by using in vitro diagnostic reagents and instruments, etc. outside the human body. Clinical doctors use IVD to diagnose diseases, guide treatment decisions, and even prevent future diseases.

Regulatory agencies have been regulating medical devices, including products for disease diagnosis. Under the current regulatory system, FDA requires that IVD products developed for the commercial market must comply with national regulatory requirements to ensure their safety and effectiveness.

IVD regulation is based on risk levels and can be divided into three categories. If the test poses relatively low risks to patients and public health, it is classified as the lowest Level I (such as cholesterol testing). Medium-risk testing (such as pregnancy testing) is classified as Level II, while Level III, the highest risk level, is reserved for tests that pose serious potential risks when performed improperly (such as gene testing used to select cancer therapy). These categories correspond to increasing levels of regulatory scrutiny, with Level I exempt from pre-market requirements while most Level II and all Level III tests require some form of pre-market review before use in humans.

IVD needs to demonstrate its safety and effectiveness through type testing and clinical validation, which are the primary standards for determining testing accuracy. The focus of type testing is to ensure that the test can measure specific analytes correctly and reliably, while clinical trials evaluate the clinical status of the validated product in specific patients.

What is LDT and how is it regulated?

The main difference between FDA-reviewed IVD and LDTs is in their development units and usage purposes. LDTs are designed and used within clinical laboratories, also referred to as "in-house" tests. Although LDTs may contain the same or similar components as FDA-reviewed tests, they must be developed and used within the same unit. Historically, FDA considered LDTs to pose lower risks to patients than most commercial diagnostic test kits, so they were exempt from almost all regulatory requirements imposed by the FDA.

In the past, most LDTs were relatively simple single analyte screens or tests developed for diagnosing rare diseases, in which case the lack of demand hindered the development of commercial IVDs. These tests were small-scale and made from legally sold clinical-use ingredients, usually used by healthcare professionals who work directly with patients. LDTs may use instruments and components or rely on complex algorithms and software to generate results and clinical interpretations. However, because these tests are developed and used within research and development laboratories, they are still considered LDTs. While FDA generally does not impose regulatory requirements on LDTs, regulatory agencies have intervened in some cases to ensure patient safety.

As technology advances, manufacturers are constantly developing diagnostic tests in different ways, but the regulatory framework remains largely unchanged. IVD and LDT generally play the same roles in clinical practice but are subject to different levels of supervision.