CMS is reminding Medicare providers that the enforcement discretion period for updated HIPAA ASC X12 Version 5010 (Version 5010) standard ends March 31, 2012. All Medicare fee-for-service transactions must be in version 5010 format by April 1, 2012; transactions using 4010 formatting will be returned as unprocessable. CMS reports that the “vast majority of provider claims” already are sent to Medicare in the 5010 format.