Implementaiton Guide being updated to read: The use of “Diagnosis, Active (ordinarily: Principal)” has a specific meaning in the 2014 measures for hospitals and should be consistent with its definition in the Uniform Hospital Discharge Data Set (UHDDS) as "that condition established after study to be chiefly responsible for occasioning the admission of the patient to the hospital for care". It refers to the Principal Diagnosis of an episode of care, as defined above. This is typically determined at or after discharge time by a coder, and is used for the billing transaction. In EHRs, the Principal Diagnosis is typically chosen from among the diagnoses that were active during the encounter and if consistent with the UHDDS definition should be labeled as “Principal. For the purpose of measure computation, the principal diagnosis should be considered to start during the episode of care. Admission and discharge diagnoses cannot be expressed using current data elements and will be expressed using timing of active diagnoses at the start or end of the episode of care. The admission or discharge diagnoses recorded by the provider should not be used as a substitute for the principal diagnosis unless they are concordant with the principal diagnosis as defined by CMS. Vendors and providers generating QRDA-1 output will need to label diagnoses appropriately to enable the measure logic to function correctly. Although it is clinically possible for the principal diagnosis to commence prior to the episode of care, the principal diagnosis should always be reported with a QRDA-I entry that starts during the episode of care.