Most measures rely at least in part on the use of various standardized codes or code systems for classifying health care provided in the United States. The measure developer should list all required codes (plus the code system and the version the codes came from) for the measure and explicitly state the source of the codes and instructions pertaining to their use. Measure developers must remember that versions of code systems should align with the time frame of testing data, which may span multiple versions of a code system. Specifications may require that certain codes accompany other codes, occur in specific locations in the record, or occur on claims from specific measured entity types. Some code sets such as the Current Procedural Terminology (CPT) may require copyright statements to accompany their use.

Some claims-based measures use Quality Data Codes (QDCs) to report quality measure data. QDCs are CPT Category II or Level II G-codes (Healthcare Common Procedure Code System). When appropriate, measured entities capture QDCs on the CMS form 1500 version 02/12. Measure specifications require use of codes, so measure developers must identify the QDCs when developing measure specifications as they would other codes (e.g., International Classification of Diseases, 10th Revision, Clinical Modification codes) for determining numerators and denominators.