Health IT & Interoperability

MPIMaster Patient Index

A database that maintains one unique, accurate identity for each patient across all of an organization's systems.

Reviewed June 2026 by Enterprise Health

Key facts

  • Maintains one unique identity per patient across systems.
  • Reconciles duplicate or conflicting records.
  • Foundational to an accurate system of record.

What it means

An MPI (or enterprise MPI) reconciles records so one person is not split across duplicate or conflicting identities. It is foundational to a system of record: surveillance, immunization and injury histories only stay accurate if every encounter ties back to the right single identity, even as data arrives from many feeds.

Frequently asked

What is a Master Patient Index?

A database that maintains one unique, accurate identity for each person across all of an organization's systems, reconciling duplicates so records don't fragment.

Why does an MPI matter for surveillance?

Surveillance, immunization and injury histories only stay accurate if every encounter ties to the right single identity — even as data arrives from many feeds. The MPI is what guarantees that.

A certified, interoperable system of record.

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