HL7 CSP Segment: Clinical Study Phase

The CSP (Clinical Study Phase) segment describes a single phase that a registered study patient has entered, such as a screening phase, a treatment cycle, or a follow-up period. It subdivides the patient's participation defined by the preceding CSR segment into time-bounded phases, each with its own begin and end timestamps and evaluability assessment. CSP typically appears between CSR and CSS within the clinical-study group.

Purpose

CSP exists to express the phase structure of a patient's journey through a clinical study. A study protocol commonly partitions participation into discrete phases, and CSP captures which phase a patient is in, when that phase began, when it ended, and whether the data collected during the phase is evaluable. This lets analytic systems align observations and schedules to the correct protocol phase and supports per-phase evaluability reporting.

Used in

CSP carries patient clinical-study phase data inside CSU (Unsolicited Study Data) messages. Within a CSU message the clinical-study group normally appears after PID, with CSR establishing the registration, CSP describing the study phase, and CSS describing the data-collection schedule.

• CSU — Unsolicited Study Data: see /academy/hl7/messages/csu

Field-by-field reference

Source: HAPI HL7v2 v2.5.1 javadocs (CSP.html). Length is shown as —; Required and Table # are taken from the HL7 v2.5.1 standard where well-established.

Most-used fields

• CSP-1 Study Phase Identifier: the coded phase that anchors all phase-scoped data.
• CSP-2 Date/time Study Phase Began: the start boundary for aligning observations to the phase.
• CSP-3 Date/time Study Phase Ended: the close boundary, often empty while a phase is active.
• CSP-4 Study Phase Evaluability: marks whether phase data can be used for analysis.

Version differences (2.3 to 2.8.2)

• CSP was introduced alongside CSR and CSS in HL7 v2.3 to support the CSU unsolicited study-data message.
• Through 2.3.1, 2.4, 2.5, and 2.5.1 the four-field CSP structure remained stable.
• The coded fields CSP-1 and CSP-4 use CE in 2.5.1 as published in the HAPI javadocs.
• From 2.6 onward, coded fields across the standard trend toward CWE; partners on 2.7 through 2.8.2 may express CSP-1 and CSP-4 as CWE rather than CE.
• No fields have been added to or removed from CSP across these releases; the changes are data-type normalization only.

Common mistakes

• Sending CSP without a preceding CSR, leaving the phase unattached to a registered subject.
• Leaving CSP-1 Study Phase Identifier empty, which makes the phase ambiguous even though it is not strictly required.
• Populating CSP-3 on a phase that is still open; an active phase should have no end timestamp.
• Treating CSP-1 as free text rather than a coded value drawn from a protocol phase list.
• Confusing CSP-4 Study Phase Evaluability with CSR-14 Patient Evaluability Status; one is per-phase, the other per-subject.
• Assuming CE components map cleanly to CWE on partners running 2.7 or later.

Examples

Minimal CSP (phase identifier and begin time):

CSP|PHASE-SCREEN^Screening Phase^L|20260601103000

Fully populated CSP:

CSP|PHASE-TX1^Treatment Cycle 1^L|20260603080000|20260624080000|EVAL^Evaluable^L

Annotated breakdown:

CSP-1  Study Phase Identifier ...... PHASE-TX1 Treatment Cycle 1
CSP-2  Date/time Phase Began ....... 2026-06-03 08:00:00
CSP-3  Date/time Phase Ended ....... 2026-06-24 08:00:00
CSP-4  Study Phase Evaluability .... EVAL Evaluable

In context, inside a CSU unsolicited study-data message after PID:

MSH|^~&|EDC|SPONSOR|REG|SITE|20260603081500||CSU^C09^CSU_C09|MSG00512|P|2.5.1
PID|1||PT-90031^^^SPONSOR^MR||Doe^Jane^A||19710204|F
CSR|STUDY2024-ONC-17^^^SPONSOR^STUDY|||PT-90031^^^SPONSOR^MR||20260601103000
CSP|PHASE-TX1^Treatment Cycle 1^L|20260603080000

A second in-context excerpt showing a completed, evaluable phase:

MSH|^~&|EDC|SPONSOR|REG|SITE|20260624081000||CSU^C09^CSU_C09|MSG00560|P|2.5.1
PID|1||PT-90031^^^SPONSOR^MR||Doe^Jane^A||19710204|F
CSR|STUDY2024-ONC-17^^^SPONSOR^STUDY|||PT-90031^^^SPONSOR^MR||20260601103000
CSP|PHASE-TX1^Treatment Cycle 1^L|20260603080000|20260624080000|EVAL^Evaluable^L

FHIR mapping

CSP is not mapped at the segment level. No segment-level ConceptMap is published in the v2-to-FHIR IG for CSP. Conceptually, CSP aligns with the FHIR ResearchSubject resource and references a ResearchStudy phase: the phase identifier in CSP-1 corresponds to a protocol phase within ResearchStudy, and the begin and end timestamps in CSP-2 and CSP-3 can populate a ResearchSubject progress period. These are implementer conventions, not a published normalized mapping.

Engine considerations

• Confirm the engine carries CSP within its CSU C09 structure or accepts it as a generic specialty segment.
• All four CSP fields are non-repeating, so no repetition handling is required, but TS timezone preservation in CSP-2 and CSP-3 matters.
• Order matters: route CSP only when its parent CSR is present, since CSP has no patient identifier of its own.
• When transforming CE to CWE for a 2.7+ partner, map identifier, text, and coding-system components for CSP-1 and CSP-4.
• An open phase should be emitted with CSP-3 empty; do not default it to the message timestamp.

How Vorro parses and produces CSP

• On inbound CSU messages, Vorro reads CSP positionally per the HAPI v2.5.1 structure and associates each CSP with the most recent CSR in the group.
• CSP-2 and CSP-3 are normalized to a primary internal timestamp form with timezone retained and re-rendered to HL7 TS on output.
• CSP-1 and CSP-4 are parsed as coded elements; Vorro can emit them as CE or transform to CWE for partners on 2.7 or later via a configurable rule.
• A CSP with an empty CSP-3 is preserved as an open phase rather than being auto-closed.
• Phase ordering is retained so multiple CSP occurrences within a subject reproduce in their original sequence.

Related pages

• /academy/hl7/segments/csr
• /academy/hl7/segments/css
• /academy/hl7/messages/csu

Sources

• CSP segment javadoc (HAPI HL7v2 v2.5.1)
• HAPI HL7v2 v2.5.1 API index
• HL7 v2 product brief