HL7 SIU (Scheduling Information Unsolicited) messages communicate appointment and scheduling events between systems — creating, modifying, and cancelling appointments across EHRs, practice management systems, and departmental scheduling applications.
Segment Name Required Purpose MSH Message Header Yes Sender, receiver, message type, version SCH Scheduling Activity Yes Appointment details, status, duration PID Patient Identification Yes Patient demographics and identifiers PV1 Patient Visit No Visit context RGS Resource Group Yes Groups related resources for the appointment AIS Appointment Information - Service No Service/procedure being scheduled AIG Appointment Information - General Resource No Equipment, room, or other resources AIL Appointment Information - Location No Appointment location AIP Appointment Information - Personnel No Provider/staff assigned NTE Notes and Comments No Scheduling notes
Event Name Description S12 New Appointment Notification Appointment booked S13 Appointment Rescheduled Date/time changed S14 Appointment Modified Details changed (not time) S15 Appointment Cancelled Appointment removed S16 Appointment Discontinued Recurring appointment ended S17 Appointment Deleted Permanent removal from schedule S26 Notification of Patient No-Show Patient did not arrive
Event Name Description S18 Appointment Rebook (Filler) Filler system rebooks appointment S19 Appointment Rebook (Placer) Placer system rebooks appointment S20 Notification of Cancellation (Filler) Filler-initiated cancellation S21 Notification of Blocked Schedule Time slot blocked S22 Notification of Unblocked Schedule Time slot unblocked S23 Notification of Deleted Schedule Schedule slot deleted S24 Query Trigger: Open (Filler) Open schedule slots S25 Query Trigger: Booked (Filler) Booked schedule slots
Code Meaning Booked Appointment confirmed Pending Awaiting confirmation Waitlisted On waiting list Started Patient checked in Complete Appointment finished Cancelled Appointment cancelled Noshow Patient did not show Blocked Time slot unavailable
A new appointment booking:
SCH Scheduling Activity SCH|APT78901^SCHED_SYS|APT78901^EPIC|||||ROUTINE^Routine^HL70277|OFFICE^Office Visit^LOCAL|30|MIN|^^30^202603101400^202603101430|||||ATT1234^SMITH^JANE^^^MD|^WPN^PH^^^^^555-222-3333|MAIN_CLINIC^MAIN_HOSP|ATT1234^SMITH^JANE^^^MD||Booked Field Name Value Note SCH-1 Placer Appointment ID APT78901^SCHED_SYS SCH-2 Filler Appointment ID APT78901^EPIC SCH-8 Appointment Type ROUTINE^RoutineStandard scheduled visit SCH-9 Duration 30 SCH-10 Duration Units MIN SCH-11 Timing ^^30^202603101400^202603101430March 10, 2026 at 2:00-2:30 PM SCH-25 Filler Status BookedAppointment confirmed
PID Patient Identification PID|1||MRN12345^^^MAIN_HOSP^MR||DOE^JOHN^ALEXANDER||19800115|M|||123 MAIN ST^^ANYTOWN^OH^44101||^PRN^PH^^^^^555-867-5309 Field Name Value Note PID-3 Patient Identifier List MRN12345^^^MAIN_HOSP^MR PID-5 Patient Name DOE^JOHN^ALEXANDER
PV1 Patient Visit PV1|1|O|MAIN_CLINIC^EXAM3^01^MAIN_HOSP||||ATT1234^SMITH^JANE^^^MD
RGS Resource Group RGS|1|A Field Name Value Note RGS-2 Action Code AAdd — new resource group
AIS Service Resource AIS|1|A|OFFICE_VISIT^Office Visit^LOCAL|||202603101400|0|MIN|30|MIN Field Name Value Note AIS-3 Service OFFICE_VISIT^Office VisitOffice visit service AIS-7 Start Date/Time 2026031014002:00 PM AIS-10 Duration 30 MIN
AIP Personnel Resource AIP|1|A|ATT1234^SMITH^JANE^^^MD|ATT^Attending^HL70443 Field Name Value Note AIP-3 Personnel ATT1234^SMITH^JANE^^^MDDr. Jane Smith AIP-4 Role ATT^AttendingAttending provider
AIL Location Resource AIL|1|A|MAIN_CLINIC^EXAM3^01^MAIN_HOSP||202603101400|0|MIN|30|MIN Field Name Value Note AIL-3 Location MAIN_CLINIC^EXAM3^01^MAIN_HOSPExam Room 3 at Main Clinic
Many scheduling integrations are bi-directional — appointments created in either system must sync to the other. This requires:
Matching on appointment IDs (SCH-1 placer vs SCH-2 filler numbers)
Conflict detection when both systems modify the same appointment
A clear “source of truth” designation for each appointment type
Handling of simultaneous updates (last-write-wins vs merge logic)
SIU interfaces often need to sync provider availability alongside appointments. S21 (Blocked Schedule) and S22 (Unblocked Schedule) events communicate provider time-off, meeting blocks, and other unavailable periods. These events prevent double-booking when multiple systems manage the same provider’s schedule.
HL7 v2 has limited native support for recurring appointments. Most implementations handle recurrences by sending individual S12 events for each occurrence, linked by a series identifier in the SCH segment or a custom Z-segment. The S16 (Discontinued) event terminates the remaining appointments in a series.
HL7 Workbench Parse and validate SIU messages online with segment highlighting and field lookup.