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National Health Advisory- Notification of Possible duplication of 'WA - WC' series NHI Numbers


There is a small risk that WA-WC series NHI numbers may be duplicated and display data associated with two people within the same record. A medical warning (see below) is being applied to the affected range of WA-WC series NHI numbers.


The Ministry is aware of a potential problem with issuing "W" series National Health Index (NHI) numbers.

The NHI system has been issuing these numbers nationally since 16 March 2018, but it has been brought to our attention that a block of 46,000 "W" series numbers was assigned by Whakatane hospital in the 1990s, prior to their local systems being integrated with the national NHI system  

These numbers were all deactivated and a process was undertaken to strip this data out of health sector systems more than a decade ago. All affected individuals at that time were set up with new NHI numbers in the national system.  However, it appears some numbers have been included on paper documentation and subsequently entered into DHBs' systems (e.g. lab and radiology systems) at the time.  In these cases it is possible that two patients (one recent and one historical) may be sharing data under a single NHI.

The exact size of the problem is uncertain and at this point indications are that only a small subset of the WA, WB, WC pre-fix numbers assigned by Whakatane may present any risk.

As an immediate response the Ministry has changed the NHI to stop issuing numbers in the range that were previously issued by Whakatane.  This will prevent any further identity confusion.

As a follow up action the Ministry has commenced work with stakeholders to quantify the size of the issue and determine an appropriate remediation / communication strategy.  This includes adding a Medical Warning to the range of affected NHIs to alert medical professionals to the risk of incorrectly linked historic lab results. This is a timely reminder for health professionals to always verify that the results they are looking at relate to the person in front of them.

The Medical Warning is:

WA, WB, WC NHI numbers may be duplicates that are incorrectly linking to lab system data from the 1990's. Please check that lab results you see relate to the patient in front of you and notify the lab of any inconsistencies. 

The Ministry will communicate further about the results of the assessment and proposed actions next week when we have more detailed information.


Last updated : Thursday, August 30, 2018

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