^O21
OML^O21 — Laboratory Order
OML^O21 is the modern laboratory order message introduced in HL7 v2.5 as the recommended replacement for ORM^O01 in lab ordering workflows. It includes a dedicated SPM (Specimen) segment that explicitly describes the specimen required, making it more precise for LIS-facing interfaces.
When Is This Sent?
Sent when placing a specimen-based lab order in a LIS-capable system. Fired by the CPOE or EHR when the clinician places a lab order requiring a physical specimen (blood, urine, tissue).
Real-World Usage
OML^O21 is mandated by IHE Laboratory Testing Workflow (LTW) profile and is the preferred lab order message for modern LIS deployments. The SPM segment eliminates ambiguity about specimen type and collection requirements. Hospitals transitioning from ORM^O01 to OML^O21 often do so when upgrading their LIS — both systems must support the new message type before migration.
Message Structure
Segment names link to their field-level reference pages.
| # | Segment | Purpose in this message | Req | Repeat |
|---|---|---|---|---|
| 1 | MSH | Message header with OML^O21 in MSH.9 | R | — |
| 2 | PID | Patient demographics including MRN | R | — |
| 3 | ORC | Order common segment — ORC.1 specifies action (NW=New, CA=Cancel) | R | — |
| 4 | OBR | Observation request — lab test code and ordering provider | R | — |
| 5 | SPM | Specimen details: specimen type, collection method, collection date/time | R | Yes |
| 6 | PV1 | Patient visit context (inpatient/outpatient) | O | — |
| 7 | DG1 | Clinical indication/ordering diagnosis | O | Yes |
| 8 | NTE | Order notes and special instructions | O | Yes |
| 9 | OBX | Pre-existing observations relevant to the order (e.g., height/weight) | O | Yes |
Example Message
Realistic example with fake patient data. Paste into the HL7 Message Viewer to explore interactively.
1MSH||^~\&|EPIC|HOSPITAL_A|LIS|HOSPITAL_A|20260310143205||OML^O21^OML_O21|OML00001|P|2.5.1 2PID||1||123456^^^HOSP_A^MR||Smith^John^M^^Mr.||19850315|M 3PV1||1|I|4A^201^1^^^HOSP_A||||1234^Ahmed^Dr.^Khalid 4ORC||NW|ORD20260310001^EPIC|||SC||||20260310143205|1234^Ahmed^Dr.^Khalid 5OBR||1|ORD20260310001^EPIC||85025^CBC with Auto Differential^CPT4|||20260310143205|||||||||1234^Ahmed^Dr.^Khalid 6SPM||1|||BLDV^Venous blood^HL70487||||||P||||||20260310143205
Troubleshooting Scenarios
LIS not creating specimen collection task after OML^O21
Cause
SPM.4 (specimen type) code is not in the LIS specimen catalog. The LIS cannot map the specimen type to a collection container or tube.
Fix
Obtain the LIS's supported specimen type codes and map your sending system's codes to them in the interface engine. Standard values come from HL7 table 0487 (Specimen Type) — verify the LIS is using standard codes or a local extension.
Orders duplicated in LIS — both ORM^O01 and OML^O21 received for same order
Cause
During a migration period, the sending system is configured to send both ORM^O01 (legacy channel) and OML^O21 (new channel) simultaneously.
Fix
Disable the legacy ORM^O01 channel to the LIS once OML^O21 is confirmed working. Use ORC.2 (placer order number) as the deduplication key — both messages will carry the same placer order number.
Common Confusions
OML^O21 (lab order with specimen) vs ORM^O01 (legacy general order). OML^O21 has the SPM segment for explicit specimen description; ORM^O01 encodes specimen details in OBR fields. Also: OML^O21 vs OMG^O19 — OML is specifically for lab/specimen-based orders; OMG^O19 is for general clinical orders that don't require a specimen (e.g., imaging, consults).
Related Message Types
Segment Reference
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