Hospital services

The NIHSI contains de-identified records from 2010–11 to 2020–21 for emergency department and admitted patient care:

  • National Hospital Morbidity Database (NHMD) – public hospital admitted patient separations in 6 participating states/territories (NSW, Victoria, South Australia, Queensland, Tasmania and the ACT) and separations for private hospitals (where available) for Victoria (2010–11 to 2016–17), the ACT (2010–11 to 2018–19) and Queensland (2010–11 to 2020–21). Supplementary codes for chronic conditions are available from 2015–16 to 2020–21.
  • National Non-Admitted Patient Emergency Department Care Database (NNAPEDC) – emergency department (ED) presentations in the 6 participating states/territories as above.

Since private hospital separations were not available for all states/territories, the analysis of hospital services only included public hospital episodes.

Treatment of admitted patient and emergency department data

Hospital data are episodic in nature, meaning that, while from the person’s perspective they may have had one hospital stay with some moves between hospitals, wards or wings, from a data collection perspective the patient had several adjoining individual episodes of care with an admission date and separation date for each (referred to here as ‘hospital episodes’). This is useful for measuring activity in the system but does not readily capture a full hospital stay.

To represent hospital care from the patient’s perspective, the analyses were based on a set of rules to combine individual hospital episodes into distinct hospital stays. Episodes belonging to the same person were identified using the unique person identifier obtained through the data linkage process. This information, along with data on episode start and end dates and modes of admission and discharge, allowed hospital episodes for an individual to be combined into one hospital stay, from first admission to final discharge.

The steps used to combine hospital episodes into hospital stays are outlined in more detail in a previous report, Younger onset dementia - New insights using linked data: Technical document (AIHW 2022).

Reasons for ED presentation

There are known gaps in the completeness of ED data relating to dementia (AIHW 2020). The major diagnostic block category was the most complete field available for exploring the reasons for ED presentation. The principal and additional diagnosis codes for dementia were also analysed (see Table 1), but counts were small and are only presented for some of the larger geographies. The report simplified the reasons for ED presentation into plain English terms (Table 8).

Table 8: Urgency related group major diagnostic block codes used to report reasons for ED presentation

Two-character diagnoses

Urgency related major diagnostic block classification

Terminology in this study


Injury, multiple sites



Injury, single site, major



Injury, single site, minor



Circulatory system illness

Circulatory diseases


Respiratory system illness

Respiratory diseases


Neurological system illness

Nervous system disease

Note: For complete list of urgency related group major diagnostic block codes see

Principal diagnoses

The International Classification of Diseases (ICD) is the World Health Organization’s internationally accepted classification of diseases and related health conditions. The 10th revision, Australian modification (ICD-10-AM) is used in this analysis. The principal diagnosis is the condition or cause that, after study, was established as the reason for the person needing care. Diagnoses are captured slightly differently between various hospitals or hospital systems (using various editions of ICD-10-AM, ICD-9-Clinial Modification and SNOMED CT-AU), but these can be mapped to the ICD-10-AM.

The principal diagnoses reported here use the ICD-10-AM diagnosis codes. Each code identifies particular conditions, symptoms, abnormal findings or causes, and the chapters in ICD-10-AM group these into broad categories. The report simplified the most common reasons into plain English terms that each correspond to a chapter, except Dementia or delirium which is reported as a separate category from Mental and behavioural disorders and Nervous system diseases (Table 9).

Table 9: ICD-10-AM codes used to report principal diagnoses for hospital stays


Disease classification

ICD diagnosis codes within range

Report terminology


Diseases of the nervous system (excluding dementia or delirium)

G00-G99 (excluding G30, G31)

Nervous system diseases


Dementia or delirium

F00, F01, F02, F03, F05, F107, F137, F187, G30, G31 and R41



Diseases of the circulatory system


Circulatory diseases


Diseases of the respiratory system


Respiratory diseases


Injury, poisoning and certain other consequences of external causes



Note: Analysis of total hospital stays excluded dialysis (ICD-10-AM ‘Z49’). Further information is available at: Episode of care—principal diagnosis, code (ICD-10-AM 10th edn) ANN{.N[N]} (