Master patient index

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The Master Patient Index (MPI) (also Master Person Index) is a database that is maintained by a health care organization for the purpose of identifying a patient and their medical record.


The MPI began as a paper based card file system that was arranged alphabetically by the patient’s last name. In larger institutions, the patient was assigned a medical record number and this number was linked to the patient’s chart. The medical record number became the unique identifier for patients being treated at a facility. It was used to avoid duplication at patient registration in order to provide connection to one authentic record.(1) As institutions became computerized, an increasing amount of data was housed in the MPI. This data now includes demographics and visit information.

Data Elements

The data elements suggested for use in an MPI to index and search records that have been recommended by AHIMA (American Health Information Management Association) are:

  • Internal patient Identification
  • Patient Name
  • DOB
  • DOB qualifier
  • Gender
  • Race
  • Ethnicity
  • Address
  • Alias/pervious name
  • SS#
  • Facility identification
  • Universal patient identifier (if available)
  • Account number
  • Admission date
  • Discharge date
  • Service type
  • Patient disposition

An MPI may also contain non-patient data elements such as guarantors, healthcare practitioners, payers, employers, and others. If more than two centers in an organization use the same database, it may be called an Enterprise Master Patient Index or EMPI.(2)

Data Integrity

The integrity of the MPI must be maintained in order for it to function correctly. An accurate MPI consists of only one medical record number for each person. Errors at registration are the usual cause of MPI inaccuracies. The three problems that most often occur at registration are duplicate medical record numbers, overlap and overlay. A duplicate medical record number exists when one person has two or more different medical record numbers within one organization. An overlap occurs when a person has more than one medical record number within an integrated delivery network or enterprise, and an overlay happens when two patients are assigned the same medical record number.(3)

Regular audits of the MPI database must be done in order to identify any errors before they are compounded. The unique identification of a patient within an organization is the first step in making sure that data is consistent and comparable.(4)


  1. AHIMA. "Fundamentals for Building a Master Patient Index/Enterprise Master Patient Index (Updated)." Journal of AHIMA (Updated September 2010).
  2. AHIMA. "Reconciling and Managing EMPIs (Updated)." Journal of AHIMA 81, no.4 (April 2010): 52-57.
  3. AHIMA. “Managing the Integrity of Patient Identity in Health Information Exchange.” Journal of AHIMA 80, no. 7 (July 2009): 62–69.
  4. Shortliffe, E. H. & Camino, E.J. (Eds.). (2006). Biomedical Informatics (p. 505). USA: Springer Science + Business Media, LLC.

Submitted by Katherine Hopkins