National Health Index data dictionary

Data Dictionary (version 5.3)

Published online: 
01 July 2009

The National Health Index (NHI) is the cornerstone of health information in New Zealand. It was established to provide a mechanism for uniquely identifying every healthcare user (HCU) by assigning each a unique number (known as the NHI number).

The purposes of the NHI include use:

  • by health and disability support services to link health data pertaining to an individual to that individual to avoid mis-assignment of health and disability support information, for example, the wrong laboratory test results
  • by health and disability support services to improve patient privacy protection when transferring an individual’s health data – for example, the receipt of laboratory test results by general practitioners
  • by the Ministry of Health, in an encrypted form, so that data can be used for statistical purposes to report on the state of health of the New Zealand population, and to assist in the development of more effective services
  • by health and disability support services to submit to, or access information from, the Medical Warnings System, for adverse drug warnings and other forms of medical alerts
  • by health and disability support services to identify previous health events, and the possible location of medical records through the Medical Warnings System.

As a registration system, the NHI includes only information needed to identify healthcare users, such as name, address (including domicile code), date of birth, sex and ethnicity. A limited amount of clinical information is available to authorised users of the NHI via the associated Medical Warning System (MWS).

The first national register was the National Master Patient Index, implemented in 1977. This was replaced with the NHI in 1993. Newborn babies have been registered on the national system since 1992.

Coverage is estimated to be 98 percent of the population.

When duplicate records for a healthcare user are identified, they are linked, one of their NHI numbers will be deemed to be the primary (or master), and the others become secondary NHI numbers. For the analysis of healthcare information relating to a unique individual, the primary NHI number should be used. Local systems may use secondary NHI numbers.

Publishing information

  • Date of publication:
    01 July 2009
  • Ordering information:
    Only soft copy available to download
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