FDA defines the term laboratory developed test (LDT) as an in vitro diagnostic test (IVD) that is intended for clinical use and designed, manufactured and used within a single laboratory.  In 1976, the Medical Device Amendments (MDA) was enacted and amended the Federal Food, Drug, and Cosmetic Act (FD&C Act) to create a system for the regulation of medical devices intended for human use.  Although considered IVDs, the FDA chose to exercise enforcement discretion for LDTs with the justification that these tests were relatively simple, used only in the lab that developed the tests and were used for rare conditions.