HL7 SIU Message: Scheduling Information

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	Add Service/Resource	Service or resource added to an appointment
S19	Modify Service/Resource	Service or resource on an appointment modified
S20	Cancel Service/Resource	Service or resource on an appointment cancelled
S21	Discontinue Service/Resource	Service or resource on an appointment discontinued
S22	Delete Service/Resource	Service or resource on an appointment deleted
S23	Blocked Schedule Slot(s)	Schedule time slot(s) blocked
S24	Opened Schedule Slot(s)	Previously blocked time slot(s) re-opened
S25	Schedule Query (SQM/SQR)	Schedule query message and response — a query pair (SQM^S25/SQR^S25), not an SIU notification

Code	Meaning
Booked	Appointment confirmed
Pending	Awaiting confirmation
Waitlist	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:

Browse the full HL7 sample messages catalog for more SIU examples — each one ready to copy as valid HL7 or download as a .hl7 file.

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. S23 (Blocked Schedule Slots) and S24 (Opened Schedule Slots) 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.