A laboratory developed test (LDT) is any test that has been developed by an individual laboratory, often using instruments and/or reagents that have not been approved by the FDA for use as/in an in vitro diagnostic test. For example, measuring pH using a pH meter and pH calibrators from a scientific supply company is an LDT. So is performing a spun hematocrit, measuring acylcarnitines by tandem mass spectrometry, or performing newborn screening on dried blood spots. Even using an FDA-approved assay for samples or in a manner not specified by the manufacturer makes that assay an LDT. If you look around your lab, you may find that you’re performing an LDT without really thinking about it.
Who regulates these tests? The FDA regulates in vitro diagnostic testing, and LDTs fall under their purview. Until recently the FDA has used “enforcement discretion” and has essentially allowed CLIA regulations and CLIA oversight to ensure proper validation and monitoring of LDTs. CLIA regulation Subpart K, Section 493.1253 gives the specific parameters that must be properly validated in any non-FDA-approved assay. CLIA also regulates the proper usage and control of LDTs, just like any test performed in the laboratory. Is it necessary for LDTs to be regulated more highly than this?
In June of 2010 the FDA announced its intention of taking a more active role in LDT regulation in the future. They also held a public meeting to discuss their increased oversight. All laboratories which perform LDTs will do well to monitor developments in this newly intended enforcement of the FDA’s role, and keep abreast of changes coming out in the regulatory environment for these tests.