For a number of key data categories in MU eCQMs, the HIT-SC has indicated that while there is a preferred code system identified, transitional code systems may be used. In these cases implementors are not expected to capture content in all the code systems, they may choose to use a single code system that is noted to be transitional. But it should be noted that code systems identified as transitional should over time be used to transition to the preferred code system. The best place to see these transitional code systems is in the CMS Measures Management Blueprint at http://www.cms.gov/Medicare/Quality-Initiatives-Patient-Assessment-Instruments/MMS/MeasuresManagementSystemBlueprint.html