The principal diagnosis must be determined in accordance with the Australian Coding Standards. Each episode of admitted patient care must have a principal diagnosis and may have additional diagnoses. The diagnosis can include a disease, condition, injury, poisoning, sign, symptom, abnormal finding, complaint, or other factor influencing health status.
As a minimum requirement the Principal diagnosis code must be a valid code from the current edition of the International statistical classification of diseases and related health problems, 10th revision, Australian modification (ICD-10-AM).
For episodes of admitted patient care, some diagnosis codes are too imprecise or inappropriate to be acceptable as a principal diagnosis and will group to an error DRG in the Australian Refined Diagnosis Related Groups.
Australian Coding Standard 0050 Unacceptable principal diagnosis codes provides guidance as to those codes that cannot be assigned.
Diagnosis codes starting with a U (only U50-U73), V, W, X or Y, describing the circumstances that cause an injury, rather than the nature of the injury, cannot be used as principal diagnosis.
Diagnosis codes within the code range U78-U88 are supplementary codes for chronic conditions and cannot be used as principal diagnosis.
Diagnosis codes within the code range U90 are healthcare associated infections and cannot be used as principal diagnosis.
Diagnosis codes which are morphology codes cannot be used as principal diagnosis.