Data classification and clinical coding
Information on the classification system used in Aotearoa New Zealand, clinical coding resources, guidelines and coding query database.
Clinical coding classifications
Clinical coding is critical to collating health data in a meaningful and efficient way.
The classification systems used in New Zealand hospitals are the:
- ICD-10-AM/ACHI/ACS classification system
- Australian Refined Diagnosis Related Groups (AR-DRG).
The ICD-10-AM/ACHI/ACS classification system collectively refers to the:
- International Statistical Classification of Diseases and Related Health Problems, Tenth Revision, Australian Modification (ICD-10-AM)
- Australian Classification of Health Interventions (ACHI)
- Australian Coding Standards (ACS).
The clinical notes from all inpatient and same day patients discharged from public hospitals are clinically coded and recorded in the hospital’s patient management system (PMS). Clinically coded summaries of these discharges are forwarded to National collections. They load and store the information in the national collection National Minimum Data Set (NMDS) for easy retrieval and analysis of the data.
National collections plays a central role in leadership and direction for national clinical coding. They make sure quality information is available for:
- casemix
- research
- health service planning
- evaluation
- funding.
In New Zealand, hospital discharge data is the basis for:
- national and regional morbidity and mortality analysis
- epidemiological research
- disease patterns and trends
- clinical research, management, and resource allocation
- supporting decisions and policy relating to health care.
The national collections team engages in activities that make sure New Zealand:
- is represented in benchmarking and information sharing with international health care organisations
- works with the classification providers in the development of ICD-10-AM/ACHI/ACS and AR-DRG.
National collections also manage the implementation of new editions of ICD-10-AM/ACHI/ACS and versions of AR-DRG for New Zealand.
ICD-10-AM is based on the International Statistical Classification of Diseases and Related Health Problems, Tenth Revision (ICD-10). This is developed by the World Health Organization and modified with permission for Australian Government purposes (ICD-10-AM).
The following products are used in New Zealand to clinically code all inpatient and same day patients discharged from our public hospitals.
- ICD-10-AM — Alphabetic Index and Tabular List of diseases and health related problems.
- ACHI — Alphabetic Index and Tabular List of interventions.
- ACS — Australian Coding Standards.
- Additional clinical coding advice and guidelines.
- National reporting requirements and clinical coding conventions.
ICD-10-AM and ACHI Alphabetic Indices and Tabular Lists contain classification conventions and instructions.
The ACS:
- are the national standards for coding of clinical data using ICD-10-AM and ACHI
- provides classification guidelines that complement ICD-10-AM and ACHI.
The use of ICD-10-AM and ACHI Alphabetic Indices and Tabular Lists, and ACS promotes consistent clinical coding of admitted episodes of care.
Extra clinical coding advice and guidelines are provided to facilitate consistent assignment and reporting of ICD-10-AM and ACHI codes where there are areas of ambiguity in the classification edition currently in use. National reporting requirements and clinical coding conventions are specific New Zealand rules and conventions for clinical coding practice. They underpin consistency and accuracy of clinical coded information submitted to the national collection National Minimum Dataset (NMDS).
Each classification edition can contain significant changes to ICD-10-AM/ACHI codes and conventions, and coding standards. It is important for data users when comparing trends over time and interpreting statistics to be aware that assumptions, code assignments and guidelines may change from one edition to another.
National collections also manage the implementation of new ICD-10-AM/ACHI/ACS editions and AR-DRG versions in New Zealand under the National Collections Annual maintenance Project (NCAMP).
For more information about the use and implementation of ICD-10-AM/ACHI/ACS in New Zealand, email us at coding_helpdesk@tewhatuora.govt.nz
The development cycle of the classification systems ICD-10-AM/ACHI/ACS and AR-DRG happened every 2 years. After a classification system review in 2020, Australia moved to a 3-year development cycle. This began with 10-AM/ACHI/ACS Twelfth Edition and AR-DRG v11.0. As part of the classification development, New Zealand is invited to take part by nominating representatives from the national collections team for 2 groups.
- The International Classification of Diseases (ICD) Technical Group (ITG). An advisory group that provides expert classification advice and technical input on ICD-10-AM/ACHI/ACS development.
- The Diagnosis Related Groups (DRG) Technical Group (DTG). An advisory group that provides expert grouping advice and technical input on AR-DRG development.
For more information about ICD-10-AM/ACHI/ACS or AR-DRG development email us at coding_helpdesk@tewhatuora.govt.nz
Classification development has been managed by several organisations since ICD-10-AM/ACHI/ACS and AR-DRG were first published.
The National Centre for Classification in Health (NCCH), University of Sydney, Australia
NCCH was responsible for the development of the following classification systems.
- ICD-10-AM/MBS-E/ACHI/ACS First Edition through to Seventh Edition. MBS-Extended was the name of the first Australian interventions classification until it was renamed to the Australian Classification of Health Interventions (ACHI) in Third Edition.
- AN-DRG/AR-DRG v3.0 to v6.0x.
This was under contract to the Australian Department of Health and Ageing (DoHA).
The National Casemix and Classification Centre (NCCC), University of Wollongong, Australia
NCCC was responsible for the development of the following classification systems.
- ICD-10-AM/ACHI/ACS Eighth Edition.
- AR-DRG v7.0.
This was under the contract of the Independent Hospital and Pricing Authority (IHPA),
The Australian Consortium for Classification Development (ACCD)
ACCD was responsible for the development of the following classification systems.
- ICD-10-AM/ACHI/ACS Ninth Edition through to Eleventh Edition.
- AR-DRG v8.0 to v10.0.
This was under the contract of the IHPA.
Independent Health and Aged Care Pricing Authority (IHACPA)
IHACPA was responsible for development of the following classification systems.
- ICD-10-AM/ACHI/ACS Twelfth Edition.
- AR-DRG v11.0.
IHACPA was previously called Independent Hospital Pricing Authority (IHPA).
Implementation dates of ICD-10-AM/ACHI/ACS in New Zealand
| Date of implementation | ICD-10-AM/ACHI/ACS edition |
| 1 July 1999 | First edition |
| 1 July 2001 | Second edition |
| 1 July 2004 | Third edition |
| 1 July 2008 | Sixth edition |
| 1 July 2014 | Eighth edition |
| 1 July 2019 | Eleventh edition |
| 1 July 2023 | Twelfth edition |
Clinical coding guidelines and resources
Clinical coding practice using ICD-10-AM/ACHI is governed by the application of the:
- Australian Coding Standards (ACS)
- IHACPA Coding Rules and FAQs, and other directives
- New Zealand clinical coding conventions and FAQs
- National Minimum Dataset (NMDS) reporting requirements.
Following these standards, rules and reporting requirements promotes clinical coding consistency. This results in the recording of quality NMDS data that are comparable at a national and international level.
Australia moved to ICD-10-AM/ACHI/ACS Thirteenth Edition 1 July 2025. But New Zealand continues to use ICD-10-AM/ACHI/ACS Twelfth Edition.
As New Zealand has not upgraded to ICD-10-AM/ACHI/ACS Thirteenth Edition all published IHACPA coding rules from July 2025 need to be reviewed for New Zealand Twelfth Edition Practice.
Provided are the IHACPA ICD-10-AM/ACHI/ACS documents that are to be referred to for New Zealand Twelfth Edition coding practice.
For IHACPA ICD-10-AM/ACHI/ACS Twelfth Edition coding rules, clinical updates and other information refer to the following.
ICD-10-AM/ACHI/ACS Twelfth Edition — IHACPAexternal link
IHACPA National Coding Advice Coding Rules and FAQs for Twelfth Edition 17 March 2025
IHACPA Retired National Coding Advice 16 December 2024
This is a summary of the current clinical coding conventions and NMDS reporting requirements for New Zealand students undertaking HIMAA clinical coding courses.
In the HIMAA Assessment and Examination Marking Guidelines section where it states ‘however, if codes are assigned they will be marked as an optional’ it means the code assignment will not be marked correct or incorrect. Marks will not be given or lost if the code(s) for the specific convention are assigned.
HIMAA assessment and examination marking guidelines for New Zealand clinical coders — July 2025
If you have a query about clinical coding, you can contact the New Zealand Coding Authority (NZCA).
We publish responses to coding queries sent to the NZCA.