Upcoming changes to NHI

The NHI numbering system is being changed to include both the current format AAANNNC (3 alpha, 3 numeric and one numeric check digit) and the new format AAANNAC (3 alpha, 2 numeric, 1 alpha and one alpha check digit).  Two variants of the check digit algorithm will be implemented to allow for the current NHI number format having a numeric check digit and the new format having an alphabetic check character.

The two formats will co-exist (i.e. ‘old’ format numbers will not be replaced) and the new format will not be issued until the current format has been exhausted.

This approach is detailed in the updated HISO 10046 Consumer Health Identity Standard.

We need to change the format because we are running out of NHI numbers to assign using the current format.  Approximately 16,000 NHIs are issued each month (~200,000 per annum) and we are planning to cut across to the new format on the 1^st of October 2025.

The NHI support team identified a preferred option in 2017 and referred this to the Health Information Standards Organisation (HISO).  In 2018 there was a formal public comment process - refer https://www.health.govt.nz/publication/nhi-number-format-change-public-comment-document.  The submissions received were overwhelming in favour of the recommended option.

Retaining the existing NHI character length and changing the alpha/numeric character sequence was deemed to be the lowest impact option available.

The new format will not be issued by the production NHI system until October 2025.

It is recommended that systems which use the NHI are changed to accommodate the new format as soon as possible.

Test NHIs will be made available in the pre-production compliance test environment to facilitate sector testing.

The NHI UAT system has been upgraded to support the new format, however the new format will not be issued by the NHI production system until 1 October 2025. 

National system changes will be planned and implemented to meet this timeline.

Systems that store the NHI number and/or interact with the NHI system will need to ensure they can accommodate both the old format and the new format.  Some systems may also need to implement the new check digit calculation if they currently perform NHI check digit validations.

In addition, because the new format will end with two alpha characters, facilities will need to ensure that these are accommodated when filing physical patient records.

It is recommended that systems are changed to accommodate the new format as soon as possible to allow a comfortable lead time before the first numbers are issued in the new format. The sequencing of changes is largely irrelevant, however all systems that use the NHI must be upgraded to accommodate the new format before 1 October 2025. 

Te Whatu Ora’s NHI UAT compliance environment supports the new format and test NHI numbers. Compliance tests are available to support sector testing. 

Please contact Integration@health.govt.nz for further detail.

Te Whatu Ora will not fund software vendors to implement support for the new NHI format. 

It is expected that software vendors will absorb this cost and/or it will be dealt with as a contractual issue between the software user and the software provider on the basis that the NHI represents a fundamental health system standard and that vendors are generally paid maintenance and support fees to cover changes of this nature.

Implementation and testing of the new check digit algorithm identified a weakness with the algorithm which means it failed to identify an unacceptably high number of character substitutions.  In recognition that we have one chance to get this right before the new NHI number format starts to be issued, we have changed the check digit algorithm to use a modulus 23 operator, rather than a modulus 24 operator, retaining the existing sequence of factors (7, 6, 5, 4, 3, 2).  This will reduce character substitution detection failures from an unacceptably high rate of 7%, to approximately 0.2%. Importantly, it also resolves an issue where “1” and “7” could be freely substituted in the number section of the NHI.

Not every IT system that stores the NHI validates the check digit, however those that do will need to ensure they are using a modulus 23 operator, rather than a modulus 24 operator, when calculating the check sum.  An updated version of the HISO 10046 Consumer Health Identity Standard was published on 20 April 2023 describing this change.

The NHI system has a number of historical gaps in the existing format range.  These gaps have been reserved for NHI pre-allocation and other purposes. 

In the event we reach the end of the current format sequence before 1 October 2025, these gaps will be used to bridge any shortfall until we start issuing new format NHI numbers.

New format NHI numbers will be issued in order of the first letter, starting with A’s, and then a randomised allocation of the next 5 characters e.g., ACA31FM, ASE37QK, ARE62RS, […] BGJ06AS, BGA44DT, BWT41BY.

The decision to issue numbers this way has been taken to minimise the incidence of identity confusion, particularly when dealing with multiple births.