Australian Casemix Glossary

The glossary gives definitions for a number of commonly used casemix related terms. It also explains the meanings of several abbreviations that appear regularly in literature dealing with Australian health services.

Page last updated: 27 May 2009

For an authoritative source of health- related definitions used in Australia, see the Data Dictionary (METeOR) compiled by the Australian Institute of Health and Welfare. The Australian Casemix glossary defines a number of casemix- related terms not covered by the National Health Data Dictionary.

Additional diagnosis

See Secondary Diagnosis.

Adjacent Diagnosis Related Group (ADRG)

One or more DRGs generally defined by the same diagnosis or procedure code list. DRGs within an ADRG have different levels of resource consumption and are partitioned on the basis of several factors. The most common are diagnoses/procedures served as a severity split, same day and PCCL. The ADRG number is the first three characters of the DRG number.

Admission date

Date on which an admitted patient commences an episode of care (HDSC 2008).

Admission weight (AdmWt)

The weight on admission to hospital, for infants aged less than one year.

Admitted patient

A patient who undergoes a hospital's admission process to receive treatment and/or care. This treatment and/or care is provided over a period of time and can occur in hospital and/or in the person’s home (for hospital in the home patients) (HDSC 2008).

Admitted Patient Care (APC) Collection

Admitted Patient Care (APC) Collection, formerly known as the National Hospital Morbidity (Casemix) database (NHMCD), is managed by the Department of Health and Ageing for National Health Care Agreements and casemix development purposes. It covers public and private hospital activity since 1991-92. Each record consists of a mix of demographic items (eg. age, sex), administrative items (eg. insurance status and mode of separation), and clinical items (eg. diagnoses and procedures).

Australian National Diagnosis Related Groups (AN-DRG)

Australia’s first national DRG classification jointly developed by 3M Australia and the Australian Government. Between 1992 and 1996, versions 1.0 to 3.1 were released.

Australian Refined Diagnosis Related Groups (AR-DRG)

Australia’s second national DRG classification developed by the Australian Government. Since 1997, versions 3.2 to 6.0 have been released.

Backward maps

In the context of AR-DRG Version 6.0, backward maps link ICD-10-AM/ACHI 6th edition codes to ICD-10-AM/ACHI 5th edition codes on the basis of clinical and coding meaning.


An information tool involving the use of scientific methods to build and make use of classifications of patient care episodes. In popular usage, the mix of types of patients treated by a hospital or other health care facility (Eagar and Hindle 1994).

Casemix is about the relationship between hospital’s activity and costs, and makes use of data about classifications that are clinically meaningful and explain variation in resource use.

CC exclusion list

The CC status of a diagnosis code can change according to the principal diagnosis and other additional diagnoses for the record and other factors such as sex and mode of separation. The CC exclusion list itemises, for each CC code, other diagnoses that would preclude the code from being treated as a CC.


A concomitant but unrelated pathologic or disease process; usually used in epidemiology to indicate the coexistence of two or more disease processes (Stedman 1990).


A morbid process or event occurring during a disease which is not an essential part of the disease, although it may result from it or from independent causes (Stedman 1990).
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Complication and comorbidity level (CCL)

CCLs are severity weights given to ALL diagnoses. They range in value from 0 to 4 for surgical and neonate episodes, and from 0 to 3 for medical episodes, and have been developed through a combination of medical judgement and statistical analysis. That is:

0 = not a complication or comorbidity
1 = a minor complication or comorbidity
2 = a moderate complication or comorbidity
3 = a severe complication or comorbidity
4 = a catastrophic complication or comorbidity

Complication and/or comorbidity (CC)

CC codes are diagnoses that are likely to result in significantly greater resource consumption.

Diagnosis Related Group (DRG)

A patient classification scheme that provides a clinically meaningful way of relating the types of patients treated in a hospital to the resources required by the hospital.

DRG cost weight

A measure of the relative cost of a DRG. Usually the average cost across all DRGs is chosen as the reference value, and given a weight of 1.

Episode of care

A period of health care with a defined start and end (HDSC 2008).

Error DRGs

In AR-DRG Version 6.0, hospital records that contain clinically atypical or invalid information are assigned to one of three error DRGs:

960Z Ungroupable
961Z Unacceptable Principal Diagnosis
963Z Neonatal Diagnosis Not Consistent W Age/Weight
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Forward maps

In the context of AR-DRG Version 6.0, forward maps link ICD-10-AM/ACHI 5th edition codes to ICD-10-AM/ACHI 6th edition codes on the basis of clinical and coding meaning.


These consist of logic and codes used by several MDCs or ADRGs within a MDC. In AR-DRG Version 6.0, functions are used to define three concepts: Major problem; Multiple major problems and Unrelated OR procedures. The Major problem and Multiple major problems are limited to MDC 15 but Unrelated OR procedures features in a number of MDCs.


The grouper is specially designed computer software that assigns hospital episodes to MDCs and DRGs, according to this classification.


The Hospital Casemix Protocol (HCP) data collection was established as part of the 1995 Private Health Insurance Reform legislation to monitor the deregulation of the private health industry.


International Statistical Classification of Diseases, 9th Revision, Clinical Modification.


International Statistical Classification of Diseases and Related Health Problems, 10th Revision, Australian Modification.

Leave days

Leave is a temporary absence from hospital, with medical approval for a period no greater than seven consecutive days. Leave days are calculated as the date returned from leave minus the date went on leave. Total leave days are the sum of the leave days for all leaves within a hospital stay (HDSC 2008).

Length of stay (LOS)

The LOS of a patient is measured in patient days. A same day patient should be allocated a LOS of one patient day. The LOS of an overnight stay patient is calculated by subtracting the date the patient is admitted from the date of separation and deducting total leave days. Total contracted patient days are included in the LOS (HDSC 2008).
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Major Diagnostic Category (MDC)

The MDC is a category generally based on a single body system or aetiology that is associated with a particular medical speciality. However, records assigned to MDCs 01, 15, 18 and 21 may have principal diagnoses associated with other categories. In AR-DRG Version 6.0, there are 23 MDCs.

Mental health legal status (MHLS)

Whether a person is treated on an involuntary basis under the relevant state or territory mental health legislation, at any time during an episode of admitted patient care, an episode of residential care or treatment of a patient/client by a community based service during a reporting period (HDSC 2008).

Involuntary patients are persons who are detained in hospital or compulsorily treated in the community under mental health legislation for the purpose of assessment or provision of appropriate treatment or care.

Mode of separation

Status at separation of a patient (discharge/transfer/death) and the place to which the patient is released (HDSC 2008).


The National Hospital Cost Data Collection (NHCDC) is an annual, voluntary collection of hospital's cost and activity data and has been established to produce annual updates of the National public and private sector cost weights for Australian Refined Diagnosis Related Group (AR-DRG) and associated analytical tables contained in the Cost Report.


National Minimum Data Set

Non-operating room (NonOR) procedures

Procedures considered significant by the classification for some MDCs. However, it is to be noted that procedures identified as NonOR for purposes of AR-DRG Version 6.0 may take place in operating rooms. If a NonOR procedure is not significant in an MDC, the patient's episode of care will be assigned to a medical DRG.

Operating room (OR) procedures

Procedures considered significant throughout AR-DRG Version 6.0. If an OR procedure is not significant in a MDC that an episode is assigned to, it will be grouped to one of the unrelated OR DRGs 801A, 801B and 801C.

Patient clinical complexity level (PCCL)

This is a measure of the cumulative effect of a patient’s complications and comorbidities, and is calculated for each episode. The calculation is complex and has been designed to prevent similar conditions from being counted more than once.
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The Private Hospital Data Bureau data collection was established in 1997 as part of the 1995 Private Health Industry Reform legislation to monitor the deregulation of the private health industry.

Principal diagnosis (PDX)

The diagnosis established after study to be chiefly responsible for occasioning an episode of admitted patient care, an episode of residential care or an attendance at a health care establishment (HDSC 2008).

Same day admission

An admission where a patient is admitted and separated on the same date.

Secondary diagnosis (SDX)

A condition or complaint either coexisting with the principal diagnosis or arising during an episode of admitted patient care, an episode of residential care or an attendance at a health care establishment (HDSC 2008).

Secondary diagnosis is also referred to as additional diagnosis.


The process by which an admitted patient completes an episode of care.

Separation date

Date on which an admitted patient completes an episode of care (HDSC 2008).

Surgical, other and medical partitions

MDCs are sub-divided into a maximum of three separate partitions, for surgical, other and medical. The presence or absence of OR and NonOR procedures is generally responsible for the assignment of a record to one or other of these partitions.

Unrelated OR DRGs

Patients whose OR procedures are unrelated to the patient’s principal diagnosis are assigned to one of three unrelated OR DRGs:

801A OR Procedures Unrelated to Principal Diagnosis W Catastrophic CC
801B OR Procedures Unrelated to Principal Diagnosis W Severe or Moderate CC
801C OR Procedures Unrelated to Principal Diagnosis W/O CC

Typically, these are patients admitted for a medical treatment; they develop a complication unrelated to the principal diagnosis and later have an OR procedure performed for the secondary diagnosis associated with the complication.

The World Health Organisation (WHO)

WHO is the directing and coordinating authority for health within the United Nations system. The WHO constitution mandates the production of international classifications on health, such as ICD-10, so that there is a consensual, meaningful and useful framework which governments, providers and consumers can use as a common language.

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