HL-7 Version 2 Message Structure

HL-7 Version 2 Message Structure

  7:42 AM    mayuravaani

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Message

Message is the smallest transferable unit in hl7 and is composed of segments. It begins with the message header Segment(MSH) and is identified by the message type and the initiating event (trigger event).

Segments 

Segments are a way of grouping of items in a logical way. Segments are clearly identified by three letters located at the beginning(Segment Identifier) and are separated by segment separators.
Here, all segments beginning with Z are reserved for locally defined messages.

Fields

The information are contained in the fields of the segments. These fields are in variable length and are separated by field separators.
For each field. a data type is defined.
Field contents can be required or optional and individual fields can be repeated.
Multi component fields are used for further sub division of a field and facilitate the transmission of logically related contents.

Abstract Message Syntax

Hl7 Messages are structured using Abstract Message Syntax to enable straight forward exchange. This describes the frequency of occurrence (cardinality) and definition (required/optional/repeatable) of control and data segments in a message.
Required segments are identified by the segment identifiers, optional segments enclosed in [], repeatable in {}.

Encoding Rules

HL7 provides a specification for the presentation of data. The separating are as follows:

Every message begins with the information about the message itself.
|   => Field Separator
^ => Component Separator
~ = Repetition Separator
\  => Escape Character
& => Subcomponent Separator 

Message Segments 

MSH => Message header
PID => patient identity
PV1 => patient visit information
NK1 => patient’s Next of Kin
EVN => event type
OBX => observation/result
AL1  => Allergy information 
DG1 => Diagnosis information 
DRG => Diagnosis related group 
PR1 => procedures
ROL => Role
IN1 => Insurance
ACC => Accident information
ROL => Role
PDA => Patient death and autopsy

Message Types

ADT => Admission Transfer Discharge
ORM => Order (Pharmacy/ Treatment)
ORU => Observation Result
BAR => (Add/ Change) Billing Account
ACK=> General Acknowledgement
DFT => Detailed Financial Transaction
MDM  => Medical Document Management 
MFN => Master Files Notification
RAS => Pharmacy/ Treatment Administration
RDE => Pharmacy/ Treatment Encoded Order
RGV => Pharmacy/ Treatment Give

Message Structure