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HL7 (Health Level Seven) is an internationally accepted set of standards that specifies the transfer and the exchange of healthcare information between healthcare organizations’ systems. HL7 standards were introduced to standardize the data transfer or exchange between healthcare systems separate from the technology that each system uses. When an event (such as a patient being admitted to a hospital) occurs, the system receives a trigger that then sends the relevant information (as a message) to other systems within the organization.

Each HL7 message is created based on a trigger event and is composed of a set of segments, with the first segment always displaying the Message Header (MSH). Segments are individual lines of data/information that start with a three-character identifier (segment ID). In this blog, we will discuss ADT messages, which play a very important role in HL7 processing, as they are the most frequently used messages.

HL7 Admit Discharge Transfer- ADT

HL7 Admit Discharge Transfer- ADT

HL7 ADT messages are very important in HL7 processing and are the most commonly used messages. They are used to communicate essential information, such as patient demographics, patient states, and visit information at a healthcare facility. HL7 ADT messages provide the system with information/data for the many different types of trigger events (registrations, cancellations, patient admissions, discharges, updates, patient data merges, etc.).

In a healthcare organization, it is necessary that all patient information is entered into an Electronic Medical Record (EMR) or a Hospital Information System (HIS). Any updates or new patient data is entered into the EMR or HIS systems and are dispersed to ancillary systems through ADT messages. This results in current patient data being synchronized across the healthcare departments/systems.

HL7 ADT Message Structure 

An HL7 ADT message is composed of segments that contain important information about trigger events. Some of the essential segments that make up an ADT message include; the PV1 (Patient Visit) segment, the PID (Patient Identification) segment, and sometimes the IN1 (insurance) segment.

Example Of A Sample ADT Message

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HL7 ADT Message Types 

ADT messages are vital in HL7 communications as they add crucial information about why the message has been sent and about the patient. For example, An ADT-A04 (patient registration) message might be sent to an EMR system, while an ADT-A05 (patient Pre-admission) message might be sent to the billing department system. The speed and urgency at which a message is sent to a particular system may depend on the different type of trigger event that is transmitted. 

There are over 50 different types of HL7 ADT messages, including: 

  • ADT-A01- patient admit
  • ADT-A02- Patient Transfer 
  • ADT-A03- Patient Discharge 
  • ADT-AO4- Patient Registration 
  • ADT-A05- Patient Pre-administration 
  • ADT-A08- Patient Information Update
  • ADT-A11- Cancel Patient Admit 
  • ADT-A12- Cancel Patient Transfer 
  • ADT-A13- Cancel Patient Discharge 

HL7 ADT Event Types

The event type is used to convey the essential trigger event information to the receiving applications/systems. For example, most ADT trigger events involve a single object, such as an admit event which then creates a message that is composed of information pertaining to a single patient or account. Other ADT event types involve relationships between one or more event types (E.g., the merge events); others involve a collection of objects that have no major interrelationship (e.g., a record-oriented location-based query). 

Below is a list of all HL7 ADT event types

  • A01- Admit/visit notification
  • A02- Transfer a patient 
  • A03- Discharge Visit 
  • A04- Register a patient 
  • A05- Pre-admit a patient 
  • A06- Change an outpatient to an inpatient
  • A07- Change an inpatient to an outpatient 
  • A08- Update patient information 
  • A09- Patient departing – tracking 
  • A10- Patient arriving – tracking 
  • A11- Cancel admit or visit notification
  • A12- Cancel Transfer 
  • A13- Cancel discharge or end visit 
  • A14- Pending admit 
  • A15- Pending transfer 
  • A16- Pending discharge
  • A17- Swap patients 
  • A18- Merge patient data 
  • A19- Patient query 
  • A20- Bed status update 
  • A21- Patient goes on a ‘leave of absence.’
  • A22-patient returns from a ‘leave of absence.’ 
  • A23- Delete a patient record 
  • A24- Link Patient data 
  • A25- Cancel pending discharge 
  • A26- Cancel pending transfer
  • A27-Cancel pending admit 
  • A28- Add person data 
  • A29- Delete person data 
  • A30- Merge person data 
  • A31- update person data
  • A32- Cancel patient arriving-tracking 
  • A33- Cancel patient departing -tracking 
  • A34- Merge patient data- patient ID only 
  • A35- Merge patient data- account number only 
  • A36- Merge patient data- patient ID and account number
  • A37- Unlink patient date 
  • A38- Cancel pre-admit 
  • A39- Merge patient -patient ID 
  • A40- Merge patient- patient identifier list 
  • A41- Merge account- patient account number
  • A42- Merge visit- visit number 
  • A43- Move patient data- patient identifier list 
  • A44- Move account information- patient account number 
  • A45- Move visit information-visit number 
  • A46- Change patient ID
  • A47- Change patient identifier list 
  • A48- Change alternate patient ID 
  • A49- Change patient account number 
  • A50- change visit number 
  • A51- change alternate visit ID
  • A52- Cancel leave of absence for a patient 
  • A53- Cancel patient returns from a leave of absence 
  • A54- Change attending doctor 
  • A55- Cancel change attending doctor 
  • A60-Update allergy data
  • A61- Change consulting doctor 
  • A62- Cancel change consulting doctor


HL7 ADT messages have a vital function in HL7, as they carry important information with regards to the patient, such as patient demographic, and they provide essential information about trigger events (such as patient visits, discharge, admissions, transfers, insurance, registration, etc.). 

If you would like to know or read more about HL7 integration in your healthcare business, click here to see how our services can help grow your healthcare business or organization. 

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