FDA treats most composite in-vitro diagnostic reagents as Class I or Class II medical devices. Importers must ensure the product has received 510(k) clearance, qualifies for an exemption, or is covered by a De Novo authorization before it can be legally marketed. FDA may detain shipments that lack proper device listing or establishment registration.

Composite reagents contain two or more chemically distinct active components formulated together to perform a diagnostic or analytical function, whereas single-analyte reagents are pure or simple chemical substances. This distinction matters for SITC and HTS classification: composite preparations fall under the NES reagent heading, while pure chemical substances are typically classified by their chemical identity in other chapters.