A large group from multiple HL7 workgroups met to clarify the difference between Principal Diagnosis and Primary Diagnosis.  This definition of Principal Diagnosis does not match the consensus definition.  In order to stamp out this longstanding confusion, the recommendation is to use the agreed "common definition" for Principal Diagnosis, as declared by CMS.

• The principal diagnosis is defined as the condition, after study, which occasioned the admission to the hospital (Source: ICD-9-CM Official Guidelines for Coding and Reporting, effective October 1, 2007, pp. 84–86) The principal diagnosis is not necessarily what brought the patient to the ER , but rather, what occasioned the admission.

Further we mush note a conflict to the definition presented on slide 3 of the attached deck. The principal diagnosis is the condition established after study to be chiefly responsible for the admission. Even though another diagnosis may be more severe than the principal diagnosis, the principal diagnosis, as defined above, is entered. Entering any other diagnosis may result in incorrect assignment of a Medicare Severity - Diagnosis Related Group.