MFN^M03 — Master File Notification: Test/Observation

Broadcast a change to the laboratory test or observation master file. Carrying segment is OM1 (General Observation) with its OM2/OM3/OM4 extensions. Typical uses: new ELISA test, unit change, pediatric reference range addition.

Purpose

M03 broadcasts an update of the LIS (Laboratory Information System) test reference set to consuming systems: HIS, EAI, clinical apps. The goal is that any system interpreting an OBX can resolve the code to its definition (unit, range, method) without hitting an external DB.

Segment structure

Structure MFN_M03: MSH, MFI, { MFE, OM1, [OM2], [OM3], [OM4] } (1..* groups).

• MFI-1 — Master File Identifier: OM1 (HL7 table 0175).
• MFI-3 — File-Level Event Code: UPD (update), REP (full replacement).
• MFE-1 — Record-Level Event Code: MAD, MDL, MUP, MUC.
• OM1-2 — Producer's Service/Test/Observation ID (internal test code).
• OM3-4 — Normal Text/Codes (textual reference ranges).

Real-world example

Adding a "Fasting Plasma Glucose" test to the LIS dictionary:

MSH|^~\&|LIS|LAB01|EHR|HOSP01|20260519080000||MFN^M03^MFN_M03|MFNM03001|P|2.5.1|||AL|NE
MFI|OM1^TEST_DICTIONARY^HL70175|LIS|UPD|20260519080000|20260519080000|AL
MFE|MUP|TST-NA-2026|20260519080000|GLUC^Fasting Plasma Glucose^L|CWE
OM1|1|GLUC^Fasting Plasma Glucose^L|||SST^Serum Separator Tube^L|||10|F|24|H||CH|||||||N
OM3|1|GLUC^Fasting Plasma Glucose^L|N|3.9-5.5|mmol/L|||||N

Application acknowledgment (MFK)

MSH|^~\&|EHR|HOSP01|LIS|LAB01|20260519080002||MFK^M03^MFK_M01|ACKM03001|P|2.5.1
MSA|AA|MFNM03001
MFI|OM1^TEST_DICTIONARY^HL70175|LIS|UPD|20260519080000|20260519080000|AL
MFA|MUP|TST-NA-2026|20260519080001|S

M03 vs M08 — why M03 is obsolete

HL7 v2.6 marked M03 "withdrawn" and split it into four more granular messages:

• M08 — Test/Observation (text) – direct M03 equivalent.
• M09 — Test/Observation Numeric.
• M10 — Test/Observation Batteries.
• M11 — Test/Calculated Observations.

In practice many French LIS and HIS still use M03 for historical compatibility — it remains documented in the 2.5.1 standard and the IHE LAB profile.

Common errors

• MFI-3 = REP with a single entry: REP means "full replacement" and the receiver's entire dictionary is purged. Use UPD for diffs.
• OM1-2 changed without MFE-1 = MDL/MAD: a modified code creates a history break in LOINC mapping.
• OM3 missing: without ranges or units, OBX cannot be interpreted by clinical alert tools.
• No LOINC mapping: OM1-7 should carry a LOINC code for interoperability; otherwise local use only.

Related master files

See also: MFN^M01, MFN^M02, MFN^M04.