Introduction to HL7 Standards: v 2.x
W. Ed Hammond
February 25, 2008

Why use data interchange standards?

• Use of standards is becoming more universal. HL7 standards are likely to be in use already
• EHRVA and the vendor community support and use HL7 standards
• As new items are collected, the HL7 standard is easier to accommodate
• Maintenance is not a cost or a problem
• Less work required for new organizations to join project
• The work is already done

Choices for data interchange

• HL7 v2.n series
• HL7 v3 standard
• Model-based
• HL7 Clinical Data Architecture
• Continuity of Care Document
• Common Document Types

Which choice?

• Version 2.x is my immediate recommendation
• Messages are straight forward and the OBX segment can carry any data content
• Version 2.x is easy and straight forward to implement
• An Implementation Manual with conformance agreement for common data elements and the use of a common terminology will provide controlled interoperability
• Version 2.6 is the latest release

Version 2.x messaging standard

• Based on an implicit information model
• Focused initially on needs of HIS, later versions expanded horizontally into other areas including ambulatory care
• Most widely used HL7 standard (>90% provider organizations)
• Events not tightly coupled to profiles
• Makes no formal attempt to define process
• Available with delimiter syntax or with XML syntax
• Most currently implemented version is v2.3
• Messages initiated by trigger events

v2.x messaging standard (2)

• Uses segments whose contents are positionally defined; segments are made up of data fields which are made up of data elements
• Fields may be repeating
• Much data sent as name-value pairs
• Accommodates any HL7 registered terminology expressed as code, name, terminology ID triplet

v2.x messaging standard (3)

• Is easy to use and understand; quick implementation
• Works well within a single enterprise where both sender and receiver are tightly bound; does not work well when sender and receiver are not connected
• Has saved money on cost of interfaces
• Will continued to be supported by HL7 in the future and will continue to be implemented by users

v2.x Functional areas

• ADT, Registration, Orders, Results, patient financial, query language, immunization reporting, clinical trials, adverse drug reactions, scheduling, referrals, medical records, patient care, problem lists and goals, waveforms, personnel management, clinical lab automation transactions, master files

Version 2.6 chapters

1. Introduction
2. Control
3. Patient Administration
4. Order Entry
5. Queries
6. Financial Management
7. Observation Reporting
8. Master Files
9. Medical Records/ Information Management
10. Scheduling
11. Patient Referral
12. Patient Care
13. Clinical Laboratory Automation
14. Application Management
15. Personnel Management
16. Non-US Claims
17. Materials Management

Appendix

1. Data Definition Tables
2. Lower Layer Protocol
3. BNF Definitions
4. Glossary

The HL7 basic "Transaction Model"

Diagram:
Trigger event: (external) admit event
Adt system sends HL7 A01 message sent to network
Lab system receives A01 message and sends back to network
Adt systems receive HL7 and sends ACK message

HL7 Message Header - MSH

Addressing the envelope:

Contents of barcode example:
Sender/Placer
Receiver/Filler
Date Time
Message Type
Trigger Type
Message Number
Version Number

HL7 Message - PID Segment

Identify the patient:

Contents of barcode example:
Patient ID
Check digit
Patient Name
Mother's Maiden Name
Gender
Date of Birth
Address
City State
Zip
County
Telephone Number

HL7 Message PV1 Segment

Define the visit or encounter:

Contents of barcode example:
Patient Location
Attending
Service

HL7 Message OBR Segment

Contents of barcode example:
Placer Order Number
Biller Order Number
Universal Service ID
Text
Local Set
Reason for Study

Principal Result Interpreter Requested DT service

HL7 Result Message (ORU)

Contents of barcode example: Data Field
Component
Segment

OBX: the flexible segment

Contents of barcode example:
A code that identifies the datatype of OBX-5
A code that identifies the data in OBX-5 (Temp Reading)
OBX-5: Data
A code that identifies the units of numerical data in OBX-5
Status
Other data fields include: date of observation, identify of provider giving observation, normal ranges, and abnormal flags

OBX: with a coded value

Contents of barcode example:
A code that identifies the datatype as a coded element
A code that identifies the data in OBX-5 (ABO Blood Group)
The code is from LOINC
OBX-5: Data, A code for Group O
The code is from SNOMED