Substances intended to detect and/or measure, in some cases producing or modifying other substances, a specific analyte of interest (e.g., enzymes, hormones). Substances used as reagents must be sufficiently pure to appropriately perform a specific analytical test. Reagents are typically used in the clinical laboratory for clinical chemistry, immunochemistry, hematology, microbiology (e.g., culture), infectious immunology, and molecular biology (e.g., nucleic acid technology) tests. (UMD)