Understanding Basic HL7 Interfaces for Effective Health Information Exchange

Health information exchange depends heavily on clear, reliable communication between systems. HL7 interfaces play a crucial role in enabling this communication, especially in healthcare environments where timely and accurate data sharing can impact patient care. This post explores the basics of HL7 interfaces, focusing on HL7 v2 interfaces and common message types like ADT, ORM, ORU, DFT, SIU, MDM, RDE, and QRY. It aims to provide healthcare technology professionals, CTOs, and technical teams with practical insights to improve their understanding and implementation of these interfaces.

Hospital server room showing network infrastructure for HL7 interfaces

What Are HL7 Interfaces and Why Do They Matter?

HL7 (Health Level Seven) interfaces are standardized message formats that allow different healthcare systems to exchange clinical and administrative data. They ensure that systems such as Electronic Health Records (EHR), Laboratory Information Systems (LIS), Radiology Information Systems (RIS), pharmacy, billing, and scheduling platforms can communicate reliably.

HL7 v2 interfaces are still the most widely used interoperability standard in hospitals and clinics worldwide. They define how messages are structured and transported between systems for workflows such as patient registration and movements, orders, results, documents, charges, and scheduling.

In most provider environments, HL7 v2 is the real-time “language” that keeps systems in sync: from admissions and orders to billing and appointments, HL7 messages make sure data flows accurately across the ecosystem.

A typical HL7 v2 interface:

• Connects two or more applications (e.g., EHR ↔ LIS, EHR ↔ billing, EHR ↔ imaging)

• Uses specific message types (ADT, ORM, ORU, DFT, SIU, etc.) and segments (MSH, PID, PV1, OBR, OBX, FT1, etc.)

• Runs over a secure transport (often TCP/IP with MLLP, sometimes across VPNs or secure tunnels)

• Is usually orchestrated by an interface engine such as Mirth/NextGen Connect, Rhapsody, Cloverleaf, or similar

By implementing well-designed HL7 interfaces, healthcare organizations can:

• Improve data consistency across systems

• Reduce manual data entry and transcription errors

• Streamline clinical and administrative workflows

• Feed analytics, reporting, and downstream integrations with cleaner, trusted data

At Data InterOps, we design and manage HL7 v2 interfaces as part of broader healthcare data integration and interoperability projects, helping providers, payers, and digital health platforms exchange information in a consistent, secure, and standards-based way.

Key HL7 v2 Message Types and Their Uses

Understanding the common HL7 v2 message types is essential for anyone working with healthcare data exchange. Each message type serves a specific purpose in clinical or administrative workflows.

1. ADT – Admission, Discharge, Transfer

The ADT interface manages patient demographic and visit information. It is often the foundation of hospital interoperability.

Common events:

• Admit / Register a patient

• Discharge or transfer between departments/locations

• Update patient demographics (address, phone, insurance, etc.)

Use cases:

• Keeping EHR, bed management, nurse call, lab, radiology, dietary, and billing systems in sync

• Ensuring all systems know who the patient is, where they are, and what encounter they belong to

Without a clean ADT feed, downstream interfaces can’t reliably match patients.

MSH|^~\&|REGADT|HOSPITAL|EHR|HOSPITAL|202511240945||ADT^A01|MSG00001|P|2.5.1
EVN|A01|202511240945
PID|1||123456^^^HOSPITAL^MR||DOE^JOHN^A||19800101|M|||123 MAIN ST^^METRO^NY^10001^USA||(555)555-1234|||S||123456789
PV1|1|I|WARD^101^1^HOSPITAL||||1234^ATTENDING^ADAM^A|||MED|||||||1234567|||||||||||||||||||||||||202511240930

2. SIU – Scheduling Information Unsolicited

The SIU interface handles appointment and scheduling information across systems.

Typical flows:

• Creating, updating, canceling appointments

• Communicating resource schedules (providers, rooms, equipment)

Use cases:

• Synchronizing scheduling between practice management, EHR, radiology, and ancillary systems

• Feeding appointment data to patient portals, reminder systems, call centers, and check-in kiosks

SIU messages support better capacity management, reduced no-shows, and a smoother patient experience.

MSH|^~\&|SCHSYS|CLINIC|EHR|CLINIC|202511240950||SIU^S12|MSG00002|P|2.5.1
SCH|APPT12345|BOOK12345||||^^^FOLLOWUP VISIT|202511251000|202511251030|||30|min|||BOOKED
PID|1||789012^^^CLINIC^MR||SMITH^JANE^L||19900515|F|||45 OAK AVE^^METRO^NY^10002^USA||(555)555-6789
PV1|1|O|CLINIC^ROOM2^1^CLINIC||||5678^CARE^CAROL^C
RGS|1
AIP|1||5678^CARE^CAROL^C^^MD|D|||202511251000|202511251030

3. ORM – Order Management

The ORM interface carries clinical orders between ordering and performing systems.

Examples:

• Lab test orders

• Radiology and imaging orders

• Cardiology, pathology, and other ancillary orders

Use cases:

• Sending orders from the EHR or CPOE to LIS, RIS, PACS, and specialty systems

• Ensuring correct order identifiers and statuses are tracked across the workflow

Good ORM interfaces reduce order errors, improve turnaround times, and support full result traceability.

MSH|^~\&|EHR|HOSPITAL|LIS|LAB|202511241000||ORM^O01|MSG00003|P|2.5.1
PID|1||123456^^^HOSPITAL^MR||DOE^JOHN^A||19800101|M
PV1|1|O|OPD^LABROOM^1^HOSPITAL||||1234^ATTENDING^ADAM^A
ORC|NW|ORD12345||PLAC12345|||1^DAY^^20251124||||1234^ATTENDING^ADAM^A
OBR|1|ORD12345|PLAC12345|^CBC PANEL^L|||202511241005||||||||1234^ATTENDING^ADAM^A|||||||F

4. ORU – Observation Result

The ORU interface carries results and observations back to consuming systems.

Examples:

• Lab test results (e.g., chemistry, hematology, microbiology)

• Radiology reports and key findings

• Vitals and other clinical observations

Use cases:

• Delivering structured and narrative results from LIS/RIS back into EHRs

• Feeding decision support, dashboards, patient portals, and quality reporting systems

Together, ORM + ORU form the classic order–result loop in many hospitals.

MSH|^~\&|LIS|LAB|EHR|HOSPITAL|202511241030||ORU^R01|MSG00004|P|2.5.1
PID|1||123456^^^HOSPITAL^MR||DOE^JOHN^A||19800101|M
PV1|1|O|OPD^LABROOM^1^HOSPITAL||||1234^ATTENDING^ADAM^A
ORC|RE|ORD12345||PLAC12345||||||1234^ATTENDING^ADAM^A
OBR|1|ORD12345|PLAC12345|^CBC PANEL^L|||202511241005
OBX|1|NM|718-7^HEMOGLOBIN^LN||13.8|g/dL|13.5-17.5|N|||F
OBX|2|NM|789-8^RBC^LN||4.8|10^6/uL|4.5-5.9|N|||F

5. MDM – Medical Document Management

The MDM interface focuses on clinical documents rather than granular observations.

Typical documents:

• Discharge summaries

• Operative and procedure notes

• Consultation and progress reports

Use cases:

• Sharing clinical documents between EHRs, document management systems, portals, and HIEs

• Ensuring key narrative reports are available to care teams regardless of where they were created

MDM is often used alongside C-CDA and FHIR DocumentReference in modern environments.

MSH|^~\&|EHR|HOSPITAL|DOCSYS|HOSPITAL|202511241100||MDM^T02|MSG00005|P|2.5.1
EVN|T02|202511241100
PID|1||123456^^^HOSPITAL^MR||DOE^JOHN^A||19800101|M
PV1|1|I|WARD^101^1^HOSPITAL||||1234^ATTENDING^ADAM^A
TXA|1|DSCHSUM|202511241045|202511241045|||1234567|DOC0001||AV|||^DISCHARGE SUMMARY|||202511241100
OBX|1|FT|^REPORT TEXT||Patient admitted with pneumonia. Completed IV antibiotics and improved clinically.||||||F

6. DFT – Detailed Financial Transaction

The DFT interface links clinical activity to billing.

Examples:

• Charges for procedures, labs, imaging, supplies, and professional services

• Adjustments and financial events tied to encounters

Use cases:

• Sending charge transactions from clinical systems to billing/RCM platforms

• Supporting accurate, timely revenue capture without manual re-entry

DFT messages are a key bridge between clinical workflows and the revenue cycle.

MSH|^~\&|EHR|HOSPITAL|BILLING|HOSPITAL|202511241115||DFT^P03|MSG00006|P|2.5.1
EVN|P03|202511241115
PID|1||123456^^^HOSPITAL^MR||DOE^JOHN^A||19800101|M
PV1|1|I|WARD^101^1^HOSPITAL||||1234^ATTENDING^ADAM^A
FT1|1|202511241000|202511241000||CG|||||99213^OFFICE VISIT^CPT|1|150.00|||1234^ATTENDING^ADAM^A
FT1|2|202511241005|202511241005||CG|||||85025^CBC PANEL^CPT|1|25.00|||1234^ATTENDING^ADAM^A

7. MFN – Master File Notification

The MFN interface keeps master data aligned across systems.

Typical content:

• Providers and staff (IDs, specialties, roles)

• Locations and departments

• Services, procedures, and fee schedules

Use cases:

• Ensuring all systems use the same provider codes, location identifiers, and service lists

• Reducing mismatches and mapping errors when messages are exchanged

MFN is especially important in multi-facility and multi-system environments.

MSH|^~\&|PROVMASTER|HOSPITAL|EHR|HOSPITAL|202511241120||MFN^M02|MSG00007|P|2.5.1
MFI|STF^STAFF MASTER FILE^HL70175|UPD|202511241120|||NE
MFE|MAD|202511241120|PROV12345|STF
STF|PROV12345|ADAM^ATTENDING^A^^MD||PHYS|A|^INTERNAL MEDICINE|||||HOSPITAL CLINIC

8. RDE – Pharmacy/Treatment Encoded Order

The RDE interface supports medication and treatment orders.

Examples:

• Medication orders from CPOE/EHR to pharmacy systems

• Infusion, therapy, and treatment regimens

Use cases:

• Enabling accurate e-prescribing and dispensing workflows

• Supporting closed-loop medication management when combined with administration records and barcode scanning

RDE messages help reduce medication errors and improve patient safety.

MSH|^~\&|EHR|HOSPITAL|PHARM|HOSPITAL|202511241130||RDE^O11|MSG00008|P|2.5.1
PID|1||123456^^^HOSPITAL^MR||DOE^JOHN^A||19800101|M
PV1|1|I|WARD^101^1^HOSPITAL||||1234^ATTENDING^ADAM^A
ORC|NW|MEDORD123||RXPLAC123|||TID^THREE TIMES DAILY|||202511241200|||1234^ATTENDING^ADAM^A
RXE|^^^AMOXICILLIN 500MG CAP||500|MG|||TID^THREE TIMES DAILY|||10|D||||||1234^ATTENDING^ADAM^A
RXR|PO^ORAL

9. QRY – Query

The QRY interface enables on-demand requests for information.

Examples:

• Querying for patient demographics

• Looking up visit, order, or result details

• Requesting specific data from a registry or repository

Use cases:

• Enabling systems to pull data when needed (rather than waiting for unsolicited messages)

• Powering point-of-care tools that need to verify data in real time

QRY messages complement the push-style behavior of ADT, ORM, ORU, and other unsolicited messages.

MSH|^~\&|PORTAL|CLINIC|EHR|CLINIC|202511241135||QRY^A19|MSG00009|P|2.5.1
QRD|202511241135|R|I|QRY12345|||1^RD|123456^^^CLINIC^MR|DEMOGRAPHICS
QRF|^^^20250101|^^^20251231

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How HL7 Interfaces Work in Practice

HL7 interfaces operate by sending structured messages between systems over a network. Each message consists of segments, fields, and components that carry specific data elements. The receiving system parses the message, validates the data, and updates its records accordingly.

Example Workflow: Patient Admission and Lab Order

1. Patient Admission: The hospital’s admission system sends an ADT^A01 message to the EHR to register the patient.

2. Order Placement: The physician places a lab order, triggering an ORM^O01 message to the lab system.

3. Result Reporting: The lab completes the test and sends an ORU^R01 message back to the EHR with the results.

4. Billing: After services are rendered, a DFT^P03 message is sent to the billing system for invoicing.

   
   

This sequence illustrates how HL7 v2 interfaces enable seamless data flow across multiple systems, reducing manual entry and errors.

Best Practices for Implementing HL7 Interfaces

Successful HL7 interface implementation requires careful planning and testing. Here are some practical tips:

• Understand the workflow: Map out clinical and administrative processes to identify which HL7 messages are needed.

• Use standard message types: Stick to widely accepted HL7 v2 message types like ADT, ORM, and ORU to ensure compatibility.

• Validate messages: Implement validation rules to catch errors before messages are processed.

• Test thoroughly: Use test environments to simulate message exchanges and verify system behavior.

• Document interfaces: Maintain clear documentation of message formats, triggers, and expected responses.

• Monitor performance: Continuously monitor interface performance to detect and resolve issues quickly.

• Plan for updates: HL7 standards evolve, so plan for regular updates and maintenance.

  
  

Challenges and Solutions in HL7 Interface Management

Despite their benefits, HL7 interfaces can present challenges:

• Complexity: HL7 v2 messages can be complex and vary between implementations.

• Data inconsistencies: Different systems may interpret data fields differently.

• Integration issues: Legacy systems may lack support for modern HL7 standards.

• Security concerns: Protecting patient data during transmission is critical.

  
  

To address these challenges:

• Use interface engines that translate and route messages efficiently.

• Establish clear data standards and governance across systems.

• Employ encryption and secure transport protocols.

• Train technical teams on HL7 standards and troubleshooting.

  
  

The Future of HL7 Interfaces and Health Data Exchange

HL7 v2 interfaces remain widely used, but newer standards like HL7 FHIR (Fast Healthcare Interoperability Resources) are gaining traction. FHIR offers more flexible, web-based data exchange methods. However, many healthcare organizations continue to rely on HL7 v2 due to existing infrastructure.

Understanding basic HL7 interfaces is essential for managing current systems and planning future upgrades. Combining HL7 v2 with emerging standards can provide a comprehensive approach to health information exchange.

Effective health information exchange depends on clear communication between systems. HL7 interfaces, especially HL7 v2 interfaces, provide a reliable way to share patient data across healthcare environments. Familiarity with message types such as ADT, ORM, ORU, DFT, SIU, MDM, RDE, and QRY helps technical teams build and maintain interfaces that support clinical workflows and administrative tasks.