HL7 ADT A33 Message: Cancel Patient Departing, Structure, Segments & Examples

The HL7 A33 message is an Admit, Discharge, Transfer (ADT) event used to cancel a previously recorded Patient Departing tracking event. Officially known as ADT A33: Cancel Patient Departing, Tracking, it belongs to the HL7 Version 2 patient administration message family.

Healthcare organizations use patient tracking events to communicate movement through departments, diagnostic areas, inpatient units, and other clinical locations. An A09 event indicates that a patient is departing as part of a tracking workflow. When that departing event is canceled, an A33 message communicates the correction to connected applications.

An A33 message does not necessarily mean that the patient was discharged, transferred, or admitted again. It cancels a tracking event, and the receiving system must interpret that cancellation within the patient's current encounter and movement history.

This guide explains HL7 A33 message structure, important segments, sample messages, field mapping, Mirth Connect implementation, acknowledgment handling, troubleshooting, and integration best practices.

What Is an HL7 ADT A33 Message?

An HL7 ADT A33 message communicates the cancellation of a previously reported Patient Departing event. It is part of the HL7 Version 2 patient tracking workflow, which includes events for patient departure, arrival, and cancellation of those notifications.

The event is particularly relevant when a departing notification was generated incorrectly, a planned movement was canceled, or an authorized system needs to reverse an existing departure tracking status.

Understanding A33 within the broader HL7 ADT messaging framework helps integration teams distinguish tracking corrections from actual patient transfers, discharges, and encounter cancellations.

Purpose of the HL7 A33 Event

A33 communicates that a previously reported patient-departing tracking event should be canceled. Receiving applications use the notification to correct the relevant tracking status without automatically changing the patient's admission or discharge state.

When Is an ADT A33 Message Generated?

An A33 notification may be generated when an A09 departure was recorded incorrectly, a patient movement was canceled, or an authorized tracking workflow determines that the departure notification must be reversed.

Which Healthcare Systems Receive A33 Messages?

Patient tracking platforms, EHRs, patient administration systems, departmental applications, and hospital operations dashboards may receive A33 notifications when they support patient movement tracking and cancellation workflows.

How A33 Supports Patient Movement Accuracy

A33 helps connected applications correct inaccurate departure statuses. Proper processing reduces inconsistencies between departmental tracking boards, patient movement histories, and the actual status of a patient encounter.

Why Accurate A33 Processing Matters

Incorrect A33 processing can leave patient tracking information inconsistent or mistakenly reverse a completed movement. Reliable integration requires accurate encounter matching, tracking event validation, and careful sequencing of movement notifications.

HL7 ADT A33 Message Structure and Segments

An HL7 ADT A33 message follows the pipe-delimited message format used by HL7 Version 2. The message header identifies the A33 trigger event, while patient identification and visit information provide the context needed to locate the appropriate tracking record.

For an HL7 v2.5 implementation, the A33 event uses the ADT_A21 message structure. The core example below contains MSH, EVN, PID, and PV1 segments. Actual required and optional segments should be validated against the specific version and interface profile.

MSH Segment: Message Header

MSH identifies the sending application, receiving application, message timestamp, trigger event, message control identifier, and HL7 version. MSH-9 identifies A33 as the patient-departing cancellation event.

EVN Segment: Event Information

EVN carries event information, including the recorded event timestamp. Receiving applications can use this information to investigate when the cancellation was issued and how it relates to previous tracking events.

PID Segment: Patient Identification

PID identifies the patient associated with the departure cancellation. Receiving systems should validate the patient identifier and assigning authority before modifying any tracking record.

PV1 Segment: Patient Visit Information

PV1 provides patient visit information, including patient class, assigned location, and visit number. These fields help receiving applications locate the correct encounter and relevant tracking history.

Optional Segments and Implementation Profiles

Additional administrative or patient information segments may be supported by a particular interface. Their use should follow the agreed HL7 implementation guide rather than assumptions based on other ADT events.

HL7 ADT A33 Message Example With Field Explanation

The following HL7 ADT A33 example illustrates a fictional patient whose previously recorded departure tracking event is being canceled. The message uses HL7 v2.5 conventions. MSH-9 identifies ADT^A33^ADT_A21, PID-3 identifies the patient, and PV1-19 identifies the associated visit.

Assume a patient was expected to depart an inpatient unit for a diagnostic procedure. The tracking application generated an A09 notification, but the departure did not proceed. The source subsequently sends A33 to cancel that tracking event.

Complete HL7 ADT A33 Sample Message

MSH|^~\&|PATIENT_TRACKING|HOSPITAL|EHR|MAIN|20261014103000||ADT^A33^ADT_A21|MSG33001|P|2.5
EVN|A33|20261014102500
PID|1||P330001^^^HOSPITAL^MR||WILSON^JAMES||19760418|M
PV1|1|I|WARD5^510^A||||1234^SMITH^ANNA||||||||||||V33001

All patient information is fictional. The message represents a cancellation of a departure tracking event, not an instruction to discharge or transfer the patient.

Explore each segment and its key fields:

MSH Segment Explained

MSH identifies PATIENT_TRACKING as the sending application and EHR as the receiver. The message type identifies A33, while the message control identifier supports acknowledgment correlation.

EVN Segment Explained

EVN identifies the cancellation event and records its timestamp. The destination can use the event information to investigate the sequence of departure and cancellation notifications.

PID-3: Patient Identifier Explained

PID-3 identifies fictional patient James Wilson using identifier P330001. The assigning authority provides additional context for matching the correct patient record.

PV1-3: Assigned Patient Location Explained

PV1-3 provides the assigned location, WARD5, room 510, bed A. The cancellation should not automatically change this authoritative location without a separate validated workflow.

PV1-19: Visit Number Explained

PV1-19 identifies encounter V33001. Receiving applications can use the visit number alongside the patient identifier to locate the relevant movement tracking history.

Important HL7 ADT A33 Fields and Mapping

Reliable HL7 A33 integration depends on correct patient identification, encounter matching, and tracking event validation. MSH-9 identifies the event, MSH-10 provides a unique message control identifier, PID-3 identifies the patient, and PV1-19 provides encounter context.

EVN-2 records the event timestamp, while PV1-3 and PV1-6 may provide location information. However, the destination should not treat these fields as instructions to reverse a completed transfer or change the current location. Clear HL7 v2 integration specifications help maintain consistent tracking behavior.

MSH-9: Identifying the A33 Trigger Event

MSH-9 identifies A33 as the cancellation event. Integration engines should route it through patient-departing tracking cancellation logic rather than transfer, discharge, or admission processing.

PID-3: Matching the Correct Patient

PID-3 contains patient identifiers and assigning authorities. The receiving application should match the complete identifier context before changing a tracking record.

PV1-19: Identifying the Encounter

PV1-19 identifies the visit associated with the cancellation. Accurate encounter matching prevents the A33 event from affecting a different patient visit or movement record.

PV1-3: Preserving Location Information

PV1-3 provides the patient's assigned location. The receiving system should not automatically change the patient's physical location simply because a departure tracking event was canceled.

EVN-2: Evaluating Event Timing

EVN-2 records the event timestamp. Integration teams can use it with authoritative tracking history to investigate delayed notifications and determine whether cancellation remains appropriate.

How HL7 ADT A33 Messages Work in Healthcare Integration

An HL7 ADT A33 workflow begins when a source application determines that a previously recorded Patient Departing event must be canceled. The source generates an A33 notification identifying the patient and relevant encounter. An integration engine validates the message and routes it to connected applications.

The destination locates the appropriate departure tracking event, verifies that cancellation is permitted, and updates its tracking state. If the patient has already completed the movement, the destination should not blindly reverse the latest location or encounter status. It should follow the approved reconciliation process.

Step 1: A Departure Tracking Event Is Recorded

A patient tracking application sends an A09 notification indicating that a patient is departing. Connected systems update their supported tracking displays and departmental movement records.

Step 2: The Departure Event Is Canceled

An authorized workflow determines that the previously reported departure should be canceled. The source generates an A33 notification identifying the affected patient and encounter.

Step 3: Validate the A33 Notification

The integration engine checks the event type, patient identifier, visit number, and message metadata. Invalid or unsupported notifications enter an exception workflow.

Step 4: Cancel the Applicable Departure Tracking State

The receiving application locates the relevant A09 event and applies its approved cancellation rules. It should not automatically reverse a completed patient transfer or discharge.

Step 5: Update Downstream Systems and Acknowledge

Connected tracking applications update their supported statuses. The destination returns an acknowledgment and records the cancellation outcome for operational monitoring and audit purposes.

How to Implement HL7 ADT A33 Messages Using Mirth Connect

Mirth Connect can receive, validate, transform, and route HL7 ADT A33 messages between patient tracking systems, EHRs, patient administration applications, and departmental platforms. A typical implementation receives an A33 notification through an MLLP listener, identifies the cancellation event, extracts patient and encounter information, and sends a request to the destination's tracking service.

Because A33 cancels a previously recorded movement notification, the destination should verify that an eligible A09 event exists. Production interfaces must also handle missing departure events, duplicate cancellations, delayed messages, and conflicts with subsequent patient movements. Organizations can use Mirth Connect development services to build and maintain these interfaces.

Configure the HL7 Source Connector

Create a Mirth Connect channel using an MLLP Listener or another supported transport. Configure inbound HL7 v2 parsing, authenticated connections, acknowledgment behavior, and appropriate message retention policies.

Filter HL7 ADT A33 Messages

Use a source filter to identify A33 notifications. Keep departure cancellations separate from actual patient transfers, discharge events, and arrival tracking cancellations.

Mirth Connect JavaScript filter:

var messageType =
    msg['MSH']['MSH.9']['MSH.9.1'].toString();

var triggerEvent =
    msg['MSH']['MSH.9']['MSH.9.2'].toString();

return messageType === 'ADT' &&
       triggerEvent === 'A33';

This filter identifies the trigger event. Production channels should additionally validate the HL7 version, sending application, and agreed interface profile.

Extract Patient and Encounter Information

Use a JavaScript transformer to extract patient identifiers, encounter information, location context, event timestamp, and message control identifier.

Mirth Connect JavaScript transformer:

function component(segment, field, part) {
    var fieldName = segment + '.' + field;
    var partName = fieldName + '.' + part;

    var fieldNode = msg[segment][fieldName];

    if (fieldNode.length() === 0) {
        return '';
    }

    return fieldNode[partName]
        .toString()
        .trim();
}

var messageType = component('MSH', 9, 1);
var triggerEvent = component('MSH', 9, 2);

var patientId = component('PID', 3, 1);
var assigningAuthority = component('PID', 3, 4);
var identifierType = component('PID', 3, 5);

var visitNumber = component('PV1', 19, 1);
var visitAuthority = component('PV1', 19, 4);
var patientClass = component('PV1', 2, 1);

var unit = component('PV1', 3, 1);
var room = component('PV1', 3, 2);
var bed = component('PV1', 3, 3);

var eventTimestamp = component('EVN', 2, 1);
var messageControlId = component('MSH', 10, 1);
var sendingApplication = component('MSH', 3, 1);
var sendingFacility = component('MSH', 4, 1);

if (messageType !== 'ADT' ||
    triggerEvent !== 'A33') {
    throw new Error('Unexpected HL7 event');
}

if (!patientId || !assigningAuthority) {
    throw new Error(
        'A33 missing patient identifier or authority'
    );
}

if (!visitNumber) {
    throw new Error(
        'A33 missing visit number required by this interface'
    );
}

if (!messageControlId) {
    throw new Error(
        'A33 missing message control identifier'
    );
}

var cancellationEvent = {
    eventType: 'A33',

    patient: {
        identifier: patientId,
        assigningAuthority: assigningAuthority,
        identifierType: identifierType
    },

    encounter: {
        visitNumber: visitNumber,
        assigningAuthority: visitAuthority,
        patientClass: patientClass
    },

    assignedLocation: {
        unit: unit,
        room: room,
        bed: bed
    },

    source: {
        application: sendingApplication,
        facility: sendingFacility
    },

    eventTimestamp: eventTimestamp,
    messageControlId: messageControlId
};

channelMap.put(
    'cancellationEvent',
    JSON.stringify(cancellationEvent)
);

This example assumes that Mirth Connect has parsed the HL7 message into its XML representation. It extracts the first occurrence of the relevant fields.

Production implementations should account for repeating patient identifiers, complete assigning-authority components, and destination-specific visit matching. Requiring PV1-19 is an example interface policy, not a universal requirement for every HL7 A33 implementation.

Transform A33 Into a Tracking Cancellation Request

Create a destination-specific payload identifying the patient, encounter, and departure event to cancel. The destination must verify the original event before changing tracking status.

Example JSON transformation:

var event = JSON.parse(
    channelMap.get('cancellationEvent')
);

var request = {
    eventType: 'A33',
    action: 'cancelPatientDeparting',

    patient: event.patient,
    encounter: event.encounter,

    trackingEventToCancel: 'A09',

    assignedLocation: event.assignedLocation,

    processingStatus: 'pending_validation',

    source: event.source,

    sourceEvent: {
        messageControlId:
            event.messageControlId,
        timestamp:
            event.eventTimestamp
    }
};

channelMap.put(
    'jsonPayload',
    JSON.stringify(request)
);

This JSON structure is illustrative and not a standardized HL7 API. The receiving service should independently validate the cancellation request and determine which original tracking record it affects.

Match the Original A09 Departure Event

Locate the relevant A09 event using the patient, encounter, movement history, and any destination-specific tracking identifier. Avoid canceling unrelated departure records for the same patient.

Configure Acknowledgment and Exception Handling

Configure the source response to reflect the agreed acknowledgment mode. Route invalid identifiers, missing original events, and conflicting movement states into a monitored exception workflow.

HL7 ADT A33 ACK Message Examples and Error Handling

HL7 acknowledgment messages allow sending applications to determine whether an A33 notification was accepted or rejected under the configured acknowledgment mode. A typical acknowledgment contains MSH and MSA segments. The ERR segment may provide additional information about validation or processing errors.

In original acknowledgment mode, AA indicates application acceptance, AE indicates an application error, and AR indicates rejection. For patient tracking cancellations, the interface agreement must distinguish successful message acceptance from completion of the underlying cancellation. A positive acknowledgment does not necessarily confirm that every connected departmental tracking application has updated its records.

Successful ACK Response: AA

An AA acknowledgment indicates application-level acceptance under the configured processing mode. MSA-2 references the original A33 message control identifier.

MSH|^~\&|EHR|MAIN|PATIENT_TRACKING|HOSPITAL|20261014103001||ACK^A33^ACK|ACK33001|P|2.5
MSA|AA|MSG33001

Application Error Response: AE

An AE acknowledgment indicates an application processing error. An unknown patient, missing encounter, or unavailable departure tracking event may prevent the cancellation.

MSH|^~\&|EHR|MAIN|PATIENT_TRACKING|HOSPITAL|20261014103002||ACK^A33^ACK|ACK33002|P|2.5
MSA|AE|MSG33001
ERR|||204^Unknown Key Identifier^HL70357|E

Application Rejection Response: AR

An AR acknowledgment indicates rejection. Unsupported event types, unauthorized source applications, or invalid message profiles may cause the destination to reject an A33 notification.

MSH|^~\&|EHR|MAIN|PATIENT_TRACKING|HOSPITAL|20261014103003||ACK^A33^ACK|ACK33003|P|2.5
MSA|AR|MSG33001

Correlate ACK Responses With Cancellation Events

MSA-2 references the original message control identifier. Integration teams use this value to correlate acknowledgments, retries, and processing results with the corresponding cancellation notification.

Handle Duplicate Messages and Retry Scenarios

Use idempotency controls and current tracking state checks before retrying. A lost acknowledgment should not result in an unrelated departure being canceled or a newer movement status being overwritten.

Common HL7 ADT A33 Integration Errors and Troubleshooting

HL7 A33 integration problems frequently involve missing A09 events, incorrect patient identifiers, inconsistent encounter numbers, and delayed cancellation notifications. A receiving system may reject an A33 event because the original departure notification was never received or because the tracking state has already changed.

Another common issue occurs when a destination incorrectly interprets A33 as a transfer cancellation or discharge reversal. This can cause incorrect location updates and inconsistencies between clinical and operational systems. Troubleshooting should examine the original message, patient and visit identifiers, tracking history, acknowledgment responses, and destination processing rules. Accurate HL7 parsing and data mapping reduces these problems.

Original A09 Departure Event Is Missing

The receiving application may not have received the original A09 notification. Check message delivery logs, tracking history, and destination identifiers before attempting cancellation.

Incorrect Patient or Visit Identifier

PID-3 or PV1-19 may not match the destination's records. Verify assigning authorities, encounter identifiers, and patient identity changes before updating the tracking state.

A33 Is Incorrectly Treated as a Transfer Cancellation

A33 cancels departure tracking, while A12cancels a transfer. Mapping both events to the same operation can incorrectly modify the patient's authoritative location.

Cancellation Arrives After Another Movement Event

A delayed A33 may arrive after an A10 arrival or another tracking event. Reconcile the event sequence instead of automatically restoring an earlier tracking status.

Duplicate A33 Notifications Cause Reprocessing

Transport retries may deliver the same cancellation multiple times. Use message identifiers and tracking event state to avoid repeated processing or unintended changes.

HL7 ADT A33 vs A09, A10, A12, and A32

HL7 Version 2 defines separate patient administration events for departure tracking, arrival tracking, and cancellation of those tracking notifications. A09 indicates Patient Departing, while A33 cancels that departure tracking event. A10 indicates Patient Arriving, and A32 cancels the arriving tracking event.

A12 is different because it cancels a patient transfer rather than a tracking notification. Although these events may share similar patient and encounter fields, their effects on clinical and operational workflows are not interchangeable.

A33 vs A09: Departure and Cancellation

A09 communicates that a patient is departing within a tracking workflow. A33 cancels a previously recorded A09 event and corrects the relevant tracking status.

A33 vs A10: Departure Cancellation and Arrival

A10 communicates arrival tracking, while A33 cancels departure tracking. Receiving applications should not assume that canceling departure also cancels a separately recorded arrival event.

A33 vs A12: Tracking and Transfer Cancellation

A12 cancels a transfer, while A33 cancels a departure tracking event. The destination should apply different processing rules to protect authoritative encounter and location information.

A33 vs A32: Departure and Arrival Cancellation

A33 cancels Patient Departing tracking, while A32 cancels Patient Arriving tracking. Both support movement corrections, but each targets a different original event.

Best Practices for Reliable HL7 A33 Integration

Reliable HL7 A33 integration requires accurate patient and encounter matching, validation of the original departure event, and controlled tracking state updates. Healthcare organizations should document how A09 and A33 messages affect departmental tracking boards, movement histories, and downstream applications.

Interfaces must account for duplicate notifications, delayed events, and patients who have already completed a movement. They should also distinguish tracking corrections from actual transfers and discharges. Strong acknowledgment handling, monitoring, and audit controls help maintain consistent patient movement information.

Validate the Original Departure Tracking Event

Confirm that the relevant A09 event exists and is eligible for cancellation. Missing or conflicting tracking records should enter a controlled reconciliation process.

Preserve Authoritative Patient Location Data

Do not automatically change the patient's assigned location when processing A33. Location changes should follow the appropriate validated patient administration event.

Apply Event Sequencing and Idempotency Controls

Use message control identifiers, timestamps, and tracking history to prevent duplicate cancellations and avoid older events overwriting more recent patient movement information.

Monitor Downstream Tracking Consistency

Check that connected departmental systems reflect the approved cancellation. Reconcile differences between tracking boards, patient administration records, and other movement applications.

Protect Patient Data and Maintain Audit Records

Use authenticated transport, appropriate access controls, and audit logging. Record cancellation requests and processing outcomes without unnecessarily exposing patient information in operational logs.

Frequently Asked Questions About HL7 ADT A33 Messages

HL7 A33 integration raises important questions about patient movement tracking, cancellation events, and the distinction between tracking notifications and actual patient transfers. Healthcare developers need to understand how A33 relates to A09, which patient and encounter identifiers are relevant, and how receiving systems should handle delayed or duplicate cancellations. The following answers address common implementation questions using HL7 Version 2 conventions. Actual requirements depend on the supported HL7 version and interface implementation guide.

Need Help With HL7 ADT A33 Integration?

Accurate patient movement tracking helps hospitals maintain consistent operational information across EHRs, patient administration platforms, and departmental systems. Taction Software supports HL7 interface development, Mirth Connect configuration, patient and encounter mapping, and healthcare application integration.

Our engineers can help organizations implement A33 cancellation workflows, validate tracking events, handle message exceptions, and establish reliable monitoring and acknowledgment procedures. Whether you are connecting a patient tracking platform to an EHR or modernizing existing ADT interfaces, controlled cancellation processing helps prevent inconsistent movement information.

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We develop HL7 A33 interfaces based on source and destination requirements, including patient matching, tracking event validation, cancellation processing, and acknowledgment handling.

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