MSH — Message Header
HL7 v2.5.1 Message Header segment reference
Defines the intent, source, destination, and framing of the message. Required as the first segment of every HL7 message.
Try it now — free, no sign-up
Paste a message containing a MSH segment into the free HL7 Online parser to see every field decoded, validated, and explained in your browser.
Open the HL7 Online parser →MSH field reference
The table below lists the commonly used fields of the MSH (Message Header) segment. Field positions follow the HL7 v2.5.1 specification.
| Field | Name | Type | Len | Use | Description |
|---|---|---|---|---|---|
| MSH-1 | Field Separator | ST | 1 | R | The character used to separate fields. Almost always "|".e.g. | |
| MSH-2 | Encoding Characters | ST | 4 | R | Characters used for component, repetition, escape, and subcomponent delimiters.e.g. ^~\& |
| MSH-3 | Sending Application | HD | 227 | O | Identifies the application that sent the message.e.g. LabSystem |
| MSH-4 | Sending Facility | HD | 227 | O | Identifies the facility of the sending application.e.g. LabFacility |
| MSH-5 | Receiving Application | HD | 227 | O | Identifies the application that should receive the message.e.g. HIS |
| MSH-6 | Receiving Facility | HD | 227 | O | Identifies the facility of the receiving application.e.g. HISFacility |
| MSH-7 | Date/Time of Message | TS | 26 | R | Date and time the message was created.e.g. 20240315120000 |
| MSH-8 | Security | ST | 40 | O | Implementation-specific security value. Often used to label synthetic or test messages.e.g. SYNTHETIC |
| MSH-9 | Message Type | MSG | 15 | R | Message code + trigger event. Example: ORU^R01 for an observation result.e.g. ORU^R01 |
| MSH-10 | Message Control ID | ST | 199 | R | Unique identifier used to match the message to its acknowledgment.e.g. MSG00001 |
| MSH-11 | Processing ID | PT | 3 | R | Indicates whether the message is production (P), debug (D), or training (T).e.g. P HL7 table 0103 |
| MSH-12 | Version ID | VID | 60 | R | HL7 version the message conforms to.e.g. 2.5.1 |
Use column: R Required · C Conditional · O Optional. Type column uses HL7 data-type codes (ST = string, NM = numeric, TS = timestamp, CX = extended composite ID, XPN = extended person name, and so on).