The FSIS Chemistry Laboratory Guidebook method titled “Screening, Determination, and Confirmation of PFAS by UPLC-MS-MS” has been expanded to include swine, poultry, and Siluriformes fish muscle in addition to the currently approved cattle muscle and plasma. The method analyzes samples for 16 different per- and polyfluorinated alkyl substances (PFAS), including perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). The method has been performed throughout fiscal year 2020 to gather data on in-plant KIS-Test positive samples of cattle muscle as described in a previous Constituent Update published on August 30, 2019. Certain swine, poultry, and Siluriformes fish muscle samples received on or after October 1, 2020 as part of the existing National Residue Program may also be analyzed for PFAS using this method. Further details about an exploratory project for this additional analysis will be available in the FY2021 Annual Sampling Plan. The updated method can be found at http://www.fsis.usda.gov/wps/portal/fsis/topics/science/laboratories-and-procedures/guidebooks-and-methods/chemistry-laboratory-guidebook. Please direct questions regarding specific elements of the updated method to AskFSIS. https://www.fsis.usda.gov/wps/portal/fsis/newsroom/meetings/newsletters/constituent-updates/archive/2020/ConstUpdate092520