The Medical Warning System (MWS) warns health care providers of known risk factors that could be important when making clinical decisions about patient care. This includes drug allergies or medical conditions.




The MWS is a value-added service closely aligned with the National Health Index. It is designed to warn health care providers of the presence of any known risk factors that may be important when making clinical decisions about patient care.



The MWS comprises the following features:

  • medical warnings incorporating adverse medical reactions and significant medical conditions
  • event summaries incorporating identification of the facility where the patient’s medical record is located

Start date

The MWS was initially part of the National Master Patient Index, implemented in 1977.

Guide for use

Specifically aimed at health care providers.

Classification codes are not fully reported and are not validated. Generally, the description of the drug and the reaction is of most interest to users.

For further details refer to the Medical Warnings System (MWS) Data Dictionary.

Collection methods – guide for providers

The responsibility for maintaining the content of the MWS rests primarily with its users, the health care providers.

The codes for Adverse Medical Reactions and Significant Medical Conditions are taken from the International Classification of Diseases manual currently in use nationally in New Zealand.

For Adverse Medical Reactions, external cause codes from the ICD-9-CM-A range E930–E949 are used.

For Significant Medical Conditions, diagnosis codes from the ICD-9-CM-A range 001–999 are used.

Frequency of updates

Ongoing, as required.

Security of data

Access to the MWS is restricted to health care providers approved by the Sector Operations.

Access to the MWS features is dependent upon a valid NHI number (also known as HCU identifier) for the healthcare user being provided.

Privacy issues

Under the Health Information Privacy Code 1994, health care users must be advised that information may be entered on the MWS and that they have the right to refuse permission for this to be entered.

National reports and publications

The Centre for Adverse Reactions Monitoring (CARM) receives information from GPs and hospitals. Eventually this will be provided directly from the MWS. CARM aims to determine which adverse reactions are life-threatening to patients.

Data provision