CMS has issued final 2018 Medicare clinical laboratory fee schedule (CLFS) rates, which are based on private payer data as mandated by the Protecting Access to Medicare Act of 2014 (PAMA).  A companion document explains changes the agency made in response to public comments on the September 2017 preliminary rates and clarifying its methodology.  In addition, CMS posted its final determinations regarding the payment basis (crosswalk or gapfill) for new and existing laboratory HCPCS codes for which CMS received no applicable payment information to calculate a private payor rate-based CLFS payment amount.