Australia Refined Diagnosis-Related Groups v4.1 (AR-DRG v4.1)

From 1 July 2000 to 30 June 2001 all events were grouped to AR-DRG4.1
From 1 July 2001 – 30 June 2005 all events were grouped to AR-DRG4.2
From 1 July 2005 to 30 June 2011 all events were grouped to AR-DRG5.0

This is in line with updating our classification system to ICD-10-AM 2nd Edition. In order to group into AR-DRG v4.1, the Ministry of Health will no longer need to map back to ICD-9-CM-A 2nd Edition for grouping purposes. We will, however, be mapping back from ICD-10-AM 2nd Edition to ICD-10-AM 1st Edition for AR-DRG v4.1.

Variables used for grouping

Data items include:

  • Diagnosis
  • Procedures
  • Sex
  • Age
  • Event end type
  • Length of stay
  • Leave days
  • Admission weight
  • Mental health legal status
  • Same-day status
  • Hours of mechanical ventilation.

The AR-DRG can take up to 20 diagnosis codes and 20 procedure codes per record.

Differences between AN-DRG v3.1 and AR-DRGs v4.1

There have been some major changes between the different classification systems. All MDCs have been affected, but several features of the classification have remained unchanged. Like AN-DRGs, AR-DRGs are organised in terms of MDCs and generally based on hierarchies of diagnoses and procedures distributed between surgical, medical and other partitions.

The following are important differences between AN-DRG v3.1 and AR-DRGs v4:

  • The numbering system, and the treatment of severity, are radically different.
  • MDCs 02,17 and 22, and also multiple trauma, have been extensively modified.
  • Some DRGs have been created, while others have been merged, resulting in a fall in the total number of DRG classes from 667 to 661. New DRGs include percutaneous coronary angioplasty, microvascular tissue transfer, endoscopic procedures for bleeding oesophageal varices, same-day HIV admissions, and opoid-use disorder and dependence.
  • Some DRGs (including tracheostomy, AMI, stroke, head injury, hip replacement, shoulder and elbow procedures, skin disorders and aftercare) have been completely restructured.
  • The majority of paediatric age splits have been changed from 10 to 13 years.
  • Some surgical hierarchies (especially in MDCs 06, 08 and 09) have been re-ordered.
  • Parallel DRGs, or surgical DRGs with the same DRG definition and severity splits, have been created for prostatectomy in MDCs 11 and 12.
  • Some variables have been modified, while others have been added. For DRG definitional purposes, intended same day has been replaced by same-day. Admission weight diagnosis codes are no longer recognised for DRG grouping purposes, and the acceptable range for actual admission weight values has been modified so that it is now 400 to 9999 grams. Finally, mental health legal status, a variable that identifies whether the patient was treated on an involuntary basis under mental health legislation, has been added to severity splits in MDC 19.

AR-DRG numbering system

The format of each AR-DRG number consists of four alphanumeric characters organised in terms of ‘ADDS’, where:

A indicates the broad group to which the DRG belongs (MDC).

DD identifies the adjacent DRG within the MDC, and the partition to which the adjacent DRG belongs. An adjacent DRG consist of one or more DRGs generally defined by the same diagnosis or procedure code list but have differing levels of resource consumption and are partitioned on the basis of several factors, including complicating diagnoses/procedures, age and/or the patient clinical complexity level.

S is a split indicator that ranks DRGs within adjacent DRGs on the basis of their consumption of resources, for example:

A = highest consumption of resources within the adjacent DRG
B = second highest consumption of resources
C = third highest consumption of resources
D = fourth highest consumption of resources
Z = no split for the adjacent DRG.

Error DRGs

Hospital records that contain clinically atypical or invalid information are assigned to one of seven Error DRGs in AR-DRG v 4.1:

  • 901Z – Extensive OR Procedure unrelated to Principal Diagnosis
  • 902Z – Non-Extensive OR Procedure Unrelated to Principal Diagnosis
  • 903Z – Prostate OR Procedure Unrelated to Principal Diagnosis
  • 960Z – Ungroupable
  • 961Z – Unacceptable Principal Diagnosis
  • 962Z – Unacceptable Obstetric Diagnosis Combination
  • 963Z – Neonatal Diagnosis Not Consistent w Age/Weight.

These error DRGs fall into three groups. Group 1 relates to the method of classification, Group 2 relates more to coding standards, and Group 3 relates to coding quality.

Group 1: 901Z, 902Z and 903Z are used when all the operating room procedures are unrelated to the MDC of the patient's principal diagnosis.

Group 2: 961Z, 962Z and 963Z are used when the principal diagnosis will not allow the episode to be assigned to a clinically coherent DRG. For example, an ICD-10-AM code may be given as a principal diagnosis, when Australian Coding Standards state that the code is unacceptable as a principal diagnosis.

Group 3: 960Z is used when the principal diagnosis is invalid, or when other essential information is missing or incorrect.

Complication and Comorbidity Levels (CCLs) and Patient Clinical Complexity Levels (PCCLs)

CCLs are severity weights given to all additional 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.

PCCLs is a measure of the cumulative effect of a patient’s complications and comorbidities, and is calculated for each episode.

This information is only an introduction. Obviously, CCLs and PCCLs are very complex concepts. Please refer to the Appendix C of the Definitions Manual for more information.


Australian Refined Diagnosis Related Groups Version 4.1 Definitions Manual. Commonwealth of Australia.

This reference can be purchased from the National Centre for Classification In Health

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