Accredited laboratories and laboratories operating in exempt states should contact their appropriate agencies to confirm any additional requirements for assessing analytical sensitivity. Analytical sensitivity is the ability of an assay to detect low concentrations of the target(s) of interest. Analytical sensitivity is closely associated with an assay's limit of detection, which is defined as the lowest concentration of an analyte that an assay can successfully detect consistently. Samples used to assess analytical sensitivity must be positive for one or more targets on the assay under investigation and must be well-characterized at a known concentration. For multiplex molecular assays that require a validation study, analytical sensitivity must be established for each analyte targeted by the assay. This should be done for each analyte individually as described in previous sections as well as with multiple targets present in a sample.