The CSS (Clinical Study Data Schedule) segment describes a scheduled data-collection time point for a registered study patient within a study phase. It expresses the protocol time point, the corresponding actual patient time point, and any quality-control codes that qualify the data gathered at that point. CSS typically follows CSP within the clinical-study group and may repeat to convey a series of scheduled time points.
Purpose
CSS exists to map a study protocol's data-collection schedule onto an individual patient's timeline. Protocols define nominal time points (for example, baseline, week 4, week 12) at which assessments are collected; CSS records both the scheduled protocol time point and the patient's actual time point, plus quality-control codes that describe the completeness or validity of the data. This allows analytic systems to align observations to the intended schedule and to flag deviations.
Used in
CSS carries patient clinical-study data-schedule information 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 (CSS.html). Length is shown as —; Required and Table # are taken from the HL7 v2.5.1 standard where well-established.
| Seq | Name | Data Type | Length | Req | Repeat | Table # | Description |
|---|---|---|---|---|---|---|---|
| CSS-1 | Study Scheduled Time Point | ce | — | O | — | — | Protocol-defined scheduled time point |
| CSS-2 | Study Scheduled Patient Time Point | ts | — | O | — | — | Patient's actual scheduled time point |
| CSS-3 | Study Quality Control Codes | ce | — | O | Y | — | Quality-control codes for the data |
Most-used fields
- CSS-1 Study Scheduled Time Point: the protocol time point that labels the data-collection event.
- CSS-2 Study Scheduled Patient Time Point: the patient's actual time point used to detect schedule deviation.
- CSS-3 Study Quality Control Codes: one or more codes qualifying the completeness or validity of the data.
Version differences (2.3 to 2.8.2)
- CSS was introduced alongside CSR and CSP 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 three-field CSS structure remained stable.
- The coded fields CSS-1 and CSS-3 use CE in 2.5.1 as published in the HAPI javadocs, and CSS-3 repeats.
- From 2.6 onward, coded fields across the standard trend toward CWE; partners on 2.7 through 2.8.2 may express CSS-1 and CSS-3 as CWE rather than CE.
- No fields have been added to or removed from CSS across these releases; the changes are data-type normalization only.
Common mistakes
- Sending CSS without a preceding CSR (and usually CSP), leaving the time point unattached to a subject and phase.
- Sending only one CSS-3 occurrence when several quality-control codes apply; CSS-3 repeats.
- Confusing CSS-1 (the nominal protocol time point) with CSS-2 (the patient's actual time point).
- Treating CSS-1 or CSS-3 as free text rather than coded values.
- Dropping the timezone on CSS-2, which obscures schedule-deviation analysis.
- Assuming CE components map cleanly to CWE on partners running 2.7 or later.
Examples
Minimal CSS (scheduled time point only):
CSS|TP-WK04^Week 4 Visit^L
Fully populated CSS (with actual time point and repeating quality-control codes):
CSS|TP-WK04^Week 4 Visit^L|20260629090000|QC-COMPLETE^Data Complete^L~QC-VERIFIED^Source Verified^L
Annotated breakdown:
CSS-1 Study Scheduled Time Point .......... TP-WK04 Week 4 Visit
CSS-2 Study Scheduled Patient Time Point .. 2026-06-29 09:00:00
CSS-3 Study Quality Control Codes ......... QC-COMPLETE Data Complete
~ QC-VERIFIED Source Verified (repeat)
In context, inside a CSU unsolicited study-data message after PID:
MSH|^~&|EDC|SPONSOR|REG|SITE|20260629091500||CSU^C09^CSU_C09|MSG00604|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
CSS|TP-WK04^Week 4 Visit^L|20260629090000|QC-COMPLETE^Data Complete^L
A second in-context excerpt showing multiple scheduled time points:
MSH|^~&|EDC|SPONSOR|REG|SITE|20260727091000||CSU^C09^CSU_C09|MSG00689|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
CSS|TP-WK04^Week 4 Visit^L|20260629090000|QC-COMPLETE^Data Complete^L
CSS|TP-WK08^Week 8 Visit^L|20260727090000|QC-PENDING^Awaiting Review^L
FHIR mapping
CSS is not mapped at the segment level. No segment-level ConceptMap is published in the v2-to-FHIR IG for CSS. Conceptually, CSS aligns with the FHIR ResearchSubject / ResearchStudy model: the scheduled time point in CSS-1 corresponds to a protocol-defined visit or milestone, and CSS-2 captures the actual occurrence. Quality-control codes in CSS-3 have no single direct FHIR element and are typically carried as extensions or observation qualifiers. These are implementer conventions, not a published normalized mapping.
Engine considerations
- Confirm the engine carries CSS within its CSU C09 structure or accepts it as a generic specialty segment.
- CSS-3 repeats; configure the engine to preserve all quality-control code repetitions rather than keeping only the first.
- Preserve the TS timezone on CSS-2 so schedule-deviation calculations remain accurate.
- Route CSS only when its parent CSR (and usually CSP) is present, since CSS 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 CSS-1 and each CSS-3 repetition.
How Vorro parses and produces CSS
- On inbound CSU messages, Vorro reads CSS positionally per the HAPI v2.5.1 structure and associates each CSS with the most recent CSP and CSR in the group.
- CSS-3 is normalized into a list so every quality-control code repetition is preserved and round-tripped on output.
- CSS-2 is normalized to a primary internal timestamp form with timezone retained and re-rendered to HL7 TS on output.
- CSS-1 and CSS-3 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.
- Multiple CSS occurrences within a subject reproduce in their original sequence so the full schedule is retained.
Related pages
- /academy/hl7/segments/csr
- /academy/hl7/segments/csp
- /academy/hl7/messages/csu
