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HL7 Identifiers (Person, Patient, Account, Visit)

Healthcare systems uses different ways to identify a person or patient within the system. Most common way is to use a Medical Record Number(MRN). Patient gets a unique MRN when he/she visits a hospital for first time. If a patient visits two facilities in a hospital network he will get unique MRN for each facility. With every MRN there would be one or more accounts associated. Account number would identify a single course of treatment or episode of care. With every Account there would be one or more Visits associated. Visit Number identify a single visit or encounter during episode of care.

Now a days, many hospital networks have build a mechanism to identify a person/patient accross facilities. These are advanced systems which implement Enterprise Marser Patient Index functionality (EMPI). One patient will have single EMPI assigned for a hospital across facilities.


Identifier Hierarchy

HL7 has provided following level of identifiers to facilitate patient/visit identification. These are very helpful in Merge/Move scenarios.

Level 4 Person PID.2 - External Id -  EMPI
Level 3 Patient PID.3 - Internal Id - MRN
Level 2 Account PID.18 - Account Number
Level 1 Visit PV1.19 - Visit Number

Following figure illustrates this hierarchy in graphical way


Identifier Hierarchy


As we go up in hierarchy, we get more aggregare data and as we go down in hierarchy, we get more atomic data.

Every person in a hospital will be identified by a EMPI. A person would be registered as patient at different facilities within hospital and will get a new MRN at that facility.
Every patient would be assigned a unique account number for a perticular care episode. Every care episode will have one or more encounters identified by Visit Number.

Following figure shows relationship between identifiers

Identifier Relationship

There will be parent-child relationship between these identifiers where each parent will have one or more child with following exceptions:

  • Visit level will not have any child
  • Person level will not have any parent



Every visit must map to single account, but an Account can have one or more visits associated with it.
Every Account must map to single Patient, but a Patient can have one or more Accoutns associated with it.
Every Patient must map to single Person, but a Person can have one or more Patients associated with it.

Every hospital system will have its own policies for assigning these identifiers, but for a good HL7 interface, a system should provide following at minimmum:

  • Either a PID.2 or PID.3 to identify a unique patient within system
  • Either a PID.18 or PV1.19 to identify a unique visit within system


If PID.2 is not implemented at hospital, an HL7 Integration Analyst could still implement an EMPI using custom patient matching within ADT interface



I appreciate honest (positive/negative) feedback.


Source Comment

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Rene Spronk on 21st Feb 2013


Id Hierarchy - be careful, rather US-centric description.e.g. PID-18 is not used elsewhere.. http://wiki.hl7.org/index.php?title=Requirements_for_an_Universal_Encounter_model


PID-18 used in some countries, PV1-19 regarded as mandatory in others, notably Germany. PID-2 only in old systems..