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MPI / EMPIMaster Patient Index / Enterprise Master Patient Index

In short

A master patient index is the service that recognizes that records in different systems belong to the same person and gives them a common identity. It helps avoid duplicate records and scattered data that reduce the accuracy of the health record. According to OpenHIE, identifying each person correctly is crucial to sharing health records across institutions.

Type
Concept
Steward
No single steward: general concept or generic technology
Reviewed
October 25, 2026

Explanation

What it is

An MPI maintains the unique identity of each person receiving care and links the records that represent that person in different systems. It is a general concept, not a standard: there are many ways to implement it.

The OpenHIE architecture calls it the Client Registry, equates it with an enterprise master patient index (EMPI) and gives it three functions:

  • maintaining a central registry of patients and their demographics, with a unique identifier for each;
  • linking registration entries that differ because of a change of address, data entry errors or missing demographics;
  • letting health workers identify the facilities where a person has received care.

OpenHIE notes that even where national identity cards exist, the unique identity of an individual must be ensured across the many systems that together make up a person's health record.

How it works

  • Matching. Compares demographics to detect potential duplicates. OpenHIE recommends configurable rules, deterministic or statistical, and a configurable blocking strategy to preselect candidates.
  • Linking and de-duplication. Joins the records that belong to the same person. The OpenHIE specification states it as a requirement ("shall"), within a list of features of which, depending on the use case, a system may support many or all.
  • Master identity. IHE PMIR describes it as the dominant identity managed centrally across many organizations, also called the "Golden Patient Identity".

Standardized implementations

IHE profiles implement the concept; they do not define it.

ProfileWhat it doesBasis
PIXCross-references identifiers from different domains (ITI-8, ITI-9, ITI-10)HL7 v2 (v3 variant)
PDQFinds patients by demographics (ITI-21)HL7 v2 (v3 variant)
PIXm 3.1.0 and PDQm 3.2.0The same functions in mobile formFHIR
PMIR 1.6.0Creates, updates and deprecates master identities, notifies changes and propagates mergesFHIR R4

Common misconceptions

  • Expecting the standard to ship the algorithm. PIX does not define enterprise policies or cross-referencing algorithms: they are local decisions.
  • Handing data quality to the MPI. In PIX, the cross-reference manager is not responsible for improving the quality of the identification information it receives; that stays with the source systems.
  • Confusing it with a national identifier. A common identifier helps, but does not remove the need to link records.
  • Merging without rules. PMIR propagates merges to data custodians, but leaves out how to handle data that references a deprecated identity.

Usage examples

  1. With the IHE PIX profile, a hospital's admission system feeds each patient's identity to the cross-reference manager (ITI-8) and other systems query the equivalent identifiers (ITI-9).

  2. The IHE PMIR 1.6.0 profile, based on FHIR R4, defines how to create, update and deprecate master identities and how to subscribe to their changes.

  3. The OpenHIE Architecture Specification (version 5.2) specifies four workflows a client registry must be able to support (creating and updating demographic records, and querying them by identifier or by demographics), although each implementation may support only the ones its use case needs.

  4. According to OpenHIE, work began in Myanmar in 2016 to pilot and implement a master patient index, with the initial scope of harmonizing data across more than 100 health record instances in HIV and TB clinics.

  5. The Digital Public Infrastructure for Health report (2023) cites a 2020 evaluation in Kenya: about 50% of facilities lacked a nationally standardized client identifier format, which limits the usefulness of a client registry.

  6. At registration, staff search for the patient by name and date of birth before creating a new record, to avoid a duplicate.

Relation to other terms

Relies on2

  • FHIRMedium

    PIXm, PDQm and PMIR offer the same functions on FHIR; an MPI can work without FHIR.

  • HL7 v2Medium

    The IHE PIX and PDQ profiles, which feed and query an MPI, are based on HL7 v2 messages; HL7 v3 and FHIR variants also exist.

Depend on this one5

  • DPI-HStrong

    The client registry is one of the canonical registries the framework includes among its core components.

  • HIEStrong

    To bring together a person's information across institutions, the HIE must resolve their identity; OpenHIE includes a client registry in its architecture.

  • OpenHIEStrong

    The client registry (MPI) is one of its registry services, although each implementation adopts only the workflows it needs.

  • IHE XDS.bMedium

    XDS.b requires a common patient identifier in the affinity domain; it can be solved with an MPI (for example, via PIX) or with a national identifier.

  • TEFCAMedium

    The QHIN Technical Framework covers patient identity resolution across networks.

Sources

  1. OpenHIE Architecture Specification 5.2 — Client Registry (CR)guides.ohie.org
  2. OpenHIE Architecture Specification — Architectureguides.ohie.org
  3. IHE ITI Technical Framework Vol. 1 — Patient Identifier Cross-referencing (PIX)profiles.ihe.net
  4. IHE ITI Technical Framework Vol. 1 — Patient Demographics Query (PDQ)profiles.ihe.net
  5. IHE — Patient Master Identity Registry (PMIR) 1.6.0profiles.ihe.net
  6. OpenHIE — Achieving a Master Patient Index in Myanmarohie.org
  7. Vital Wave, PATH and Digital Square — Digital Public Infrastructure for Health (2023)media.path.org
Health interoperability glossary