PID: Patient identification

A patient in hospital wears a wristband: their name, their date of birth, and the number that hospital knows them by. PID is that wristband written down. Every other segment in the message is about the person this one identifies.

PID carries the identity of one patient: who they are, what identifiers the sending system knows them by, and the demographics that travel with those identifiers.

The shape of one line

Where PID appears

PID appears in 121 of the 202 message structures the standard defines.

A whole message

MSH|^~\&|EPIC|STJOSEPH|LABSYS|STJOSEPH|20240314093015||ADT^A01^ADT_A01|MSG00017|P|2.5.1
EVN||20240314093000
PID|1||1000345678^^^STJOSEPH^MR~453-22-9911^^^USA^SS||CARTWRIGHT^ELEANOR^MAY^^^^L||19510822|F||2106-3|41 ORCHARD LANE^APT 2B^PORTLAND^OR^97202^USA^H||^PRN^PH^^1^503^5550142|^WPN^PH^^1^503^5550188|eng|M|CHR|100034567800
PV1|1|I|3W^312^A^STJOSEPH||||1447312^OKONKWO^ADAEZE^^^^MD|||MED||||1|||1447312^OKONKWO^ADAEZE^^^^MD|I|V100034567|SELF|||||||||||||||||||SJ||A|||20240314093000

Every field

Open this PID message in HL7 Studio

Field notes

• PID-1Set ID - PID

  Set ID numbers the PID segments within one message. It is 1 in almost every message you will see, because almost every message carries one patient. It becomes meaningful in the query responses and in ORU messages that batch several patients, where a receiver that ignores it will merge results across people.

  Open PID-1 in HL7 Studio

• PID-3Patient Identifier List

  The identifier list, and the field that causes the most integration work. It repeats, and each repetition is a CX carrying the identifier, the assigning authority in component 4, and the identifier type code in component 5. A sending system commonly puts its medical record number, a national identifier and an account-adjacent identifier in the same field, distinguished only by those two components. Match on the pair, never on the bare value in component 1: two hospitals will both issue an MRN of 1000345678 and they are not the same person.

  Open PID-3 in HL7 Studio

• PID-5Patient Name

  Patient name, repeating, with a name type code in component 7. L is the legal name and is the one to store as primary. A repetition typed A is an alias and D is a display name. Where a patient uses a name that differs from their legal one, v2.5.1 has no dedicated place for it, and the convention is a second repetition typed D. Systems that read only the first repetition will usually be right and occasionally, for the patients it matters most to, wrong.

  Open PID-5 in HL7 Studio

• PID-7Date/Time of Birth

  Date of birth, a TS. In practice it arrives as an eight-character date, but the data type permits a time and a timezone offset, and neonatal systems do send the time of birth. A parser that assumes exactly eight characters will fail on a newborn.

  Open PID-7 in HL7 Studio

• PID-8Administrative Sex

  Administrative sex, bound to table 0001. This is an administrative value, not a clinical or gender-identity one, and v2.5.1 offers no field for the others. Do not map it to FHIR Patient.gender and consider the question answered; gender identity belongs in an observation, and in later HL7 versions in dedicated segments.

  Open PID-8 in HL7 Studio

• PID-11Patient Address

  Patient address, repeating, with an address type in component 7. H is home, M is mailing, and they differ often enough that taking the first repetition gives you the wrong one for a meaningful share of patients.

  Open PID-11 in HL7 Studio

• PID-13Phone Number - Home

  Home phone number as an XTN. In v2.5.1 this field carries both the older free-text form and the newer structured components, and senders differ on which they populate. Read components 5 to 7 for country, area and local number when they are present, and fall back to component 1 when they are not.

  Open PID-13 in HL7 Studio

• PID-18Patient Account Number

  Patient account number, which ties this patient to a billing account. It is not the visit number and not the encounter identifier, though it is regularly mistaken for both. PV1-19 carries the visit number.

  Open PID-18 in HL7 Studio

• PID-29Patient Death Date and Time

  Patient death date and time, and PID-30 the death indicator. A message can carry a death date with the indicator empty, or the indicator set with no date. Treat either as an assertion of death and reconcile, because a receiving system that requires both will silently keep a deceased patient active.

  Open PID-29 in HL7 Studio

Vendor behaviour

What follows describes patterns common to these systems' standard interfaces. Every installation is configured, so confirm against the interface specification for the site you are integrating with.

Mapping to FHIR

PID maps to FHIR Patient, and the mapping is mostly clean because both are describing the same thing. The work is in PID-3: each repetition becomes one Patient.identifier, with the assigning authority becoming the identifier system and the type code becoming identifier.type. Getting that wrong collapses several identifiers into one and produces duplicate patients downstream.

Parsing pitfalls

• An empty field and an explicitly null field are different

  Two adjacent delimiters mean the sender said nothing about the field, and the receiver should leave whatever it already holds. A field containing two double quotes means the sender is asserting that the value is null, and the receiver should delete what it holds. Treating the second as the first is how a corrected record silently keeps its old value.

• Repetition and components are read in the wrong order

  The repetition separator binds more loosely than the component separator, so A^B~C^D is two repetitions of two components each, not one repetition of four. Splitting on ^ before ~ inverts the structure and is a common source of names appearing in address fields.

• Escape sequences inside a field

  A literal delimiter inside a value arrives escaped: \F\ for the field separator, \S\ for component, \T\ for subcomponent, \R\ for repetition and \E\ for the escape character itself. A patient named O\S\Brien is not a two-component name. Unescape after splitting, never before.

• Segments end with a carriage return

  HL7 v2 terminates a segment with \r, not \n or \r\n. Text editors and HTTP tooling rewrite it freely, and a message that parses in a test fixture will fail against a conformant receiver if the terminator was normalised on the way in.

• Z-segments can appear anywhere PID does

  A site-defined segment beginning with Z may sit between PID and the segment you expect next. A parser that goes by position instead of reading the segment identifier will misattribute the Z-segment content to PID.

Related

• PD1additional demographics that would not fit in PID
• PV1the visit this patient identity is attached to
• NK1next of kin and associated parties for the same patient
• MSHthe header whose sending facility scopes PID-3 assigning authorities

Message types carrying PID

PID appears in 121 message structures, belonging to 76 message types.

• ADR
• ADT24
• BAR6
• BPS
• BRP
• BRT
• BTS
• CRM
• CSU
• DFT2
• DOC
• MDM2
• OMB
• OMD
• OMG
• OMI
• OML3
• OMN
• OMP
• OMS
• ORB
• ORD
• ORF
• ORG
• ORI
• ORL3
• ORM
• ORN
• ORP
• ORR
• ORS
• ORU2
• OSR
• OUL4
• PEX
• PGL
• PPG
• PPP
• PPR
• PPT
• PPV
• PRR
• PTR
• RAR
• RAS
• RCI
• RCL
• RDE
• RDR
• RDS
• REF
• RER
• RGR
• RGV
• ROR
• RPA
• RPI2
• RPR
• RQA
• RQC
• RQI
• RQP
• RRA
• RRD
• RRE
• RRG
• RRI
• RSP7
• SIU
• SQM
• SQR
• SRM
• SRR
• VXR
• VXU
• VXX