The SLT (Sterilization Lot) segment was introduced in HL7 v2.7 as part of the sterilization messaging suite. It links a sterilization lot to the device that processed it and to the individual item or tray inside that lot. SLT is what makes traceability possible: given a patient procedure that used a specific tray, you can walk back through SLT-4 Item Identifier and SLT-3 Lot Number to the exact sterilizer, cycle, and parameters that produced it.
Purpose
SLT answers "which lot was processed on which device, and what items were in it?" Where SDD describes the cycle event, SLT enumerates the items in the lot. Multiple SLT segments typically follow a single SDD, one per traceable item, each carrying its own item identifier and bar code. SLT is the segment regulators and accreditation bodies care most about because it provides the chain of custody from cycle to instrument tray.
Used in
SLT is most commonly seen in lab automation and sterilization cycle messages:
- ESU — Equipment Status Update — used when a sterilizer reports the contents of a lot it has just processed.
- ESR — Equipment Status Request — when an OR or central sterile services system asks "what is in lot X?"
- Sterilization cycle messages grouping SCP, SDD, SLT, and STZ for a complete cycle and inventory record.
Field-by-field reference
Source: HAPI HL7v2 v2.8.1 javadocs (https://hapifhir.github.io/hapi-hl7v2/v281/apidocs/ca/uhn/hl7v2/model/v281/segment/SLT.html). Length —; Required and Table # from the HL7 v2 standard where well-established.
| Seq | Name | Data Type | Length | Req | Repeat | Table # | Description |
|---|---|---|---|---|---|---|---|
| SLT-1 | Device Number | ei | — | R | — | — | Identifier of the sterilization device. |
| SLT-2 | Device Name | st | — | O | — | — | Human-readable name of the device. |
| SLT-3 | Lot Number | ei | — | O | — | — | Identifier of the sterilization lot. |
| SLT-4 | Item Identifier | ei | — | O | — | — | Identifier of the item in the lot. |
| SLT-5 | Bar Code | st | — | O | — | — | Bar code label printed for the item. |
Most-used fields
- SLT-1 Device Number — the primary identifier joining SLT back to its SCP and SDD. Required in practice.
- SLT-3 Lot Number — the value that links SLT to the matching SDD-1; receivers index traceability records on this combination.
- SLT-4 Item Identifier — the per-instrument or per-tray identifier; the field auditors trace back from a clinical procedure.
- SLT-5 Bar Code — the printed label scanned in the OR; receivers store this verbatim for round-trip scanning workflows.
- SLT-2 Device Name — informational; useful when SLT is forwarded to systems that did not see the upstream SCP.
Version differences (2.6 to 2.8.2)
- 2.6 — SLT did not exist; per-item lot data was carried via custom Z-segments or barcode-only systems outside HL7.
- 2.7 — SLT introduced with the five fields shown above.
- 2.8 — No structural changes; clarifications about EI authority components in SLT-1, SLT-3, and SLT-4.
- 2.8.1 — Documented here; identical field set to 2.8.
- 2.8.2 — No new fields; guidance added on how repeating SLT segments under one SDD should be ordered for traceability replay.
Common mistakes
- Omitting SLT-1 Device Number — without it the segment cannot be joined to the cycle that produced the lot.
- Putting the item identifier in SLT-3 Lot Number; SLT-3 is the lot, SLT-4 is the item. Receivers will mis-attribute traceability.
- Setting SLT-3 to a value that has no matching SDD-1 in the same message; downstream traceability queries return orphans.
- Stuffing structured data into SLT-5 Bar Code; it is plain ST and must contain the literal barcode payload only.
- Sending one SLT for a multi-item lot — emit one SLT per traceable item so the audit trail is complete.
- Sending SLT to a v2.5.1 receiver; the segment did not exist before v2.7.
Examples
Minimal SLT:
SLT|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI
Fully-populated SLT:
SLT|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|LOT-20260610-014^^STERILE-CENTRAL^EI|TRAY-ORTHO-118^^CSSD-INV^EI|*TRAY-ORTHO-118*20260610*
Annotated breakdown:
SLT segment id
|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI SLT-1 Device Number (EI)
|Central OR Autoclave 7 SLT-2 Device Name
|LOT-20260610-014^^STERILE-CENTRAL^EI SLT-3 Lot Number (EI)
|TRAY-ORTHO-118^^CSSD-INV^EI SLT-4 Item Identifier (EI)
|*TRAY-ORTHO-118*20260610* SLT-5 Bar Code (literal label payload)
In-context ESU excerpt (lot manifest at cycle completion):
MSH|^~&|STERILECTRL|CSSD|LIS|LAB|20260610094500||ESU^U01^ESU_U01|MSG00001906|P|2.8.1
EQU|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|20260610094500|IDLE^Idle^HL70569
SCP|1|HOURS^Hours^HL70718|YYYYMMDDHHMM^Long^HL70529|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|MedSteam 5000XL|STEAM^Steam Autoclave^HL70667|Y^Lot Controlled^HL70136
SDD|LOT-20260610-014^^STERILE-CENTRAL^EI|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|COMPLETE^Cycle Complete^HL70667|UNLOADED^Unloaded^HL70669|200|Jordan Pierce
SLT|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|LOT-20260610-014^^STERILE-CENTRAL^EI|TRAY-ORTHO-118^^CSSD-INV^EI|*TRAY-ORTHO-118*20260610*
SLT|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|LOT-20260610-014^^STERILE-CENTRAL^EI|TRAY-GEN-441^^CSSD-INV^EI|*TRAY-GEN-441*20260610*
In-context ESU excerpt (single-item lot for a high-value implant set):
MSH|^~&|STERILECTRL|CSSD|LIS|LAB|20260610103200||ESU^U01^ESU_U01|MSG00001911|P|2.8.1
EQU|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|20260610103200|IDLE^Idle^HL70569
SCP|1|HOURS^Hours^HL70718|YYYYMMDDHHMM^Long^HL70529|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|MedSteam 5000XL|STEAM^Steam Autoclave^HL70667|Y^Lot Controlled^HL70136
SDD|LOT-20260610-022^^STERILE-CENTRAL^EI|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|COMPLETE^Cycle Complete^HL70667|UNLOADED^Unloaded^HL70669|200|Morgan Vela
SLT|STZ-AUTOCLAVE-07^^STERILE-CENTRAL^EI|Central OR Autoclave 7|LOT-20260610-022^^STERILE-CENTRAL^EI|IMPLANT-SPINE-9027^^CSSD-INV^EI|*IMPLANT-SPINE-9027*20260610*
See the ESU message page for the full trigger event and segment grouping.
FHIR mapping
No segment-level ConceptMap is published in the v2-to-FHIR IG for SLT. Conceptually, SLT-1 Device Number maps to Device.identifier; SLT-3 Lot Number maps to Substance.identifier or to a sterilization-event resource identifier; SLT-4 Item Identifier typically maps to Device.identifier of the instrument tray or to a DeviceUseStatement.device reference; SLT-5 Bar Code maps to Device.identifier.value with a barcode system URI. Sterilization data maps conceptually to FHIR Device, DeviceMetric, and Substance resources rather than to a single segment-level resource.
Engine considerations
- Treat SLT-1 Device Number as mandatory regardless of the standard's "optional" stance; it is the only join key back to SCP and SDD.
- Allow multiple SLT segments per SDD. Many engines under-allocate buffers here and silently truncate the lot manifest at the first item.
- SLT-5 Bar Code may contain embedded HL7 delimiters (commonly
*and^). Run it through your standard escape pipeline; do not assume vendors have escaped for you. - Preserve SLT order on output — auditors expect the item sequence to be stable for replay.
- Build an integrity check that verifies SLT-3 Lot Number matches the SDD-1 Lot Number it follows; orphan SLTs indicate upstream segment loss.
- For receivers on v2.5.1, transform SLT to NTE or Z-segments; the segment did not exist before v2.7.
How Vorro parses and produces SLT
Vorro treats SLT as the traceability spine. On inbound: each SLT is joined to its parent SDD using SLT-3 Lot Number, and an item-trace row is written keyed on (SLT-1, SLT-3, SLT-4). SLT-5 Bar Code is captured verbatim so that OR scan-in workflows resolve to the exact label printed on the tray. On outbound: Vorro emits one SLT per traceable item in the lot, ordered by item identifier, with SLT-1 populated from the device registry and SLT-5 generated by the labelling subsystem. Vorro flags inbound messages where SLT-3 does not match the preceding SDD-1, preventing orphan traceability records from contaminating downstream analytics.
