CTI ties an order or a result to a clinical trial. It names the sponsor's study, optionally the phase of that study the patient is in, and optionally a scheduled time point within that phase. CTI is a small optional segment — three fields — but it is the link that lets a lab result or an order be attributed to the right protocol, arm, and visit when a patient is enrolled in research. It carries no patient demographics and no result data of its own; it is purely identification context that rides alongside the segments that do.
Purpose
CTI answers three questions about an order or observation: which clinical trial does this belong to (CTI-1), which phase of that trial is the patient in (CTI-2), and which scheduled time point within the phase does this correspond to (CTI-3). Because it only adds research context, CTI is repeatable where it appears and is omitted entirely for non-trial activity.
Used in
CTI appears in order and result messages tied to clinical trials, attached as an optional, repeating segment to the order or observation groups. It is most commonly seen following observation requests in result messages such as ORU and in order messages like OML, where it appends study context to the relevant OBR group. See the messages index for the full message catalog; CTI is never the leading segment of a message.
Field-by-field reference
Source: HL7 v2.5.1 standard CTI segment definition (cross-checked against the HL7 Europe refactored segment reference). R = required, C = conditional, O = optional. Repeat = field may repeat. Length shown as — pending authoritative v2.5.1 length data. Table # shown as — unless well-established.
| Seq | Name | Data Type | Length | Req | Repeat | Table # | Description |
|---|---|---|---|---|---|---|---|
| CTI-1 | Sponsor Study ID | EI | — | R | — | — | The sponsor's identifier for the clinical trial this order/result belongs to. The core field of the segment. |
| CTI-2 | Study Phase Identifier | CWE | — | C | — | HL70597 | The phase or stage of the trial the patient has entered. Conditional: must be present when CTI-3 is valued. Carried as CE in older versions. |
| CTI-3 | Study Scheduled Time Point | CWE | — | O | — | — | A specific scheduled time point within the study phase (e.g. a protocol visit). Requires CTI-2 to be valued. Carried as CE in older versions. |
Most-used fields
CTI-1 Sponsor Study ID does the real work. It is an EI (entity identifier), so in practice it carries the study identifier plus an assigning authority that scopes it — for example a protocol number issued by the sponsor. This is the value downstream research systems key on to attribute the order or result to a trial.
CTI-2 Study Phase Identifier and CTI-3 Study Scheduled Time Point are progressively optional and dependent: CTI-3 only makes sense when CTI-2 is populated, because a time point is defined relative to a phase. Many real interfaces send CTI-1 alone.
Version differences (2.3 to 2.8.2)
- 2.3 / 2.3.1: CTI is defined as a clinical-trial identification segment associated with orders and observations; CTI-2 and CTI-3 use the CE (coded element) data type.
- 2.5 / 2.5.1: coded fields migrate toward CWE/CE usage in line with the broader coded-element changes; the three-field structure is stable.
- 2.7+: coded fields are expressed as CWE in alignment with the version's data-type modernization. The field count and meaning of CTI-1 through CTI-3 are unchanged.
- Across all versions CTI stays a three-field segment; the only material drift is the data type carrying CTI-2 and CTI-3 (CE to CWE). Receivers built for an older version treat the newer CWE components they do not recognize as ignorable.
Common mistakes
- Sending CTI-3 (time point) without CTI-2 (phase). The time point is defined relative to a phase; a lone CTI-3 is ambiguous.
- Treating CTI-1 as a plain string. It is an EI — dropping the assigning authority makes the study id non-unique across sponsors.
- Attaching CTI to the wrong group, so the trial context binds to an unrelated order or observation.
- Assuming a downstream FHIR pipeline will auto-map CTI. There is no official v2-to-FHIR map for CTI; any conversion is hand-built.
Examples
Minimal CTI (required field only):
CTI|TRIAL-2026-0007^^VORRO_SPONSOR
Fully-populated CTI:
CTI|TRIAL-2026-0007^^VORRO_SPONSOR|PHASE_II^Phase II^HL70597|VISIT_03^Week 12 Visit^L
Annotated breakdown of the fully-populated example:
CTI ← segment ID
TRIAL-2026-0007^^VORRO_SPONSOR ← CTI-1 Sponsor Study ID (EI: id ^ ^ assigning authority)
PHASE_II^Phase II^HL70597 ← CTI-2 Study Phase Identifier (CWE)
VISIT_03^Week 12 Visit^L ← CTI-3 Study Scheduled Time Point (CWE)
In-context inside an ORU^R01 (result), CTI appended to the observation group:
MSH|^~&|LAB|HOSP_B|EHR|HOSP_A|20260609131500||ORU^R01^ORU_R01|CTRL-7741|P|2.5.1
PID|1||123456^^^HOSP^MR||DOE^JOHN^A||19800101|M
OBR|1||ORD555|CBC^Complete Blood Count^L
OBX|1|NM|718-7^Hemoglobin^LN||13.5|g/dL|13.0-17.0|N|||F
CTI|TRIAL-2026-0007^^VORRO_SPONSOR|PHASE_II^Phase II^HL70597|VISIT_03^Week 12 Visit^L
In-context inside an OML^O21 (laboratory order), CTI attaching trial context to the order:
MSH|^~&|CTMS|SITE_A|LAB|HOSP_B|20260609120000||OML^O21^OML_O21|CTRL-7740|P|2.5.1
PID|1||123456^^^HOSP^MR||DOE^JOHN^A||19800101|M
ORC|NW|ORD555|||||^^^20260609120000
OBR|1|ORD555||CBC^Complete Blood Count^L
CTI|TRIAL-2026-0007^^VORRO_SPONSOR|PHASE_II^Phase II^HL70597
FHIR mapping
There is no official CTI ConceptMap in the HL7 v2-to-FHIR Implementation Guide as of 2026-06-09 — CTI does not appear in the segment maps index, and the expected ConceptMap pages return 404. The mapping below is therefore conceptual and implementation-defined, not a quote from a published map.
Conceptually, CTI's trial context lands on FHIR research resources:
| CTI field | Conceptual FHIR target |
|---|---|
| CTI-1 Sponsor Study ID | ResearchStudy.identifier (the trial); links the observation/order to ResearchSubject.study |
| CTI-2 Study Phase Identifier | ResearchStudy.phase (or an extension carrying the protocol phase) |
| CTI-3 Study Scheduled Time Point | No standard element; typically an extension or carried as ResearchSubject progress / visit context |
Because no official map exists, treat any CTI-to-FHIR transform as bespoke: pin the target resources and element paths in your own mapping spec and validate against your research data model rather than relying on the IG.
Engine considerations
- CTI is optional and repeating where it occurs. An engine must not assume exactly one CTI per group; iterate.
- Bind CTI to the correct parent group (the OBR/observation or order group it follows), not globally to the message — otherwise trial context leaks onto unrelated activity.
- Validate the conditional rule: reject or flag a CTI that carries CTI-3 without CTI-2.
- Preserve the CTI-1 assigning authority component; collapsing the EI to a bare id breaks cross-sponsor uniqueness.
- Do not expect built-in FHIR conversion. Any CTI-to-ResearchStudy/ResearchSubject mapping is a custom rule the engine operator must author.
How Vorro parses and produces CTI
On parse, Vorro reads CTI as an optional repeating segment scoped to its parent order or observation group, captures CTI-1 with its assigning authority intact, and enforces the CTI-2/CTI-3 dependency so a time point never arrives without its phase. On produce, Vorro emits CTI only for trial-associated activity, stamps CTI-1 from the configured study identifier and sponsor authority, and adds CTI-2/CTI-3 from the channel's protocol mapping. Because there is no standard FHIR map for CTI, Vorro routes trial context through an operator-defined mapping to ResearchStudy/ResearchSubject rather than an IG-supplied ConceptMap.
Related pages
- OBR — the observation request group CTI most often attaches to.
- OBX — the observation/result segment whose data CTI gives trial context to.
- ORU messages — result messages where CTI carries clinical-trial attribution.
Sources
- HL7 Version 2.5.1 product brief
- HL7 v2-to-FHIR IG — segment maps index; CTI is not present, confirming no official map
- HL7 Europe refactored segment reference — CTI
