HL7 CSS Clinical Study Data Schedule Segment
HL7 field reference CSS fields from HL7 v2.5.1 Show fields
These are the generated fields for the version selected at the top of the page. The document stays the same, but the reference panel follows that version.
Fields
CSS carries clinical-study schedule data, usually to describe where a subject is relative to planned study events.
The standard describes CSS this way: The Clinical Study Data Schedule (CSS) segment is optional depending on whether messaging of study data needs to be linked to the scheduled data time points for the study. The CSS segment enables communication of data schedules and adherence that ranges from the basic to the elaborate. Use of the segment must be planned for each implementation. Each CSS segment will subsume observation and drug administration segments that follow, indicating that they satisfy this scheduled time point.
Clinical-study segments tie a message back to a trial, phase, schedule, subject registration, and protocol-specific events. They are not general observation notes; they support trial governance and reporting.
The useful data is usually the combination of study identifiers, phase identifiers, schedule timing, and subject status. Keep protocol codes and local study IDs aligned with the system that is managing the trial.
The v2.5.1 structures show CSS in CSU_C09 - CSU - Automated time intervals for reporting like monthly. That tells you where it can appear, but the implementation guide still decides which optional fields are meaningful.
For practical interface work, read the generated field panel for datatype, required, repeatable, and table details, then use the notes below to decide what the field should mean in the receiving workflow.
CSS-1 is a timing field. Send the real source-system precision, do not pad unknown dates or times, and agree how timezone offsets are handled when time of day matters.
CSS-2 is a timing field. Send the real source-system precision, do not pad unknown dates or times, and agree how timezone offsets are handled when time of day matters.
CSS-3 carries Study Quality Control Codes for this study workflow. Populate it only when the receiver has a clear use for it, and keep the value in the datatype shape shown in the generated field panel.
This field can repeat. Use repetitions for separate real-world values, not as a workaround for putting several unrelated ideas in one field.