3: Exchange Standards
Version 2 (V2)
Version 2 (V2), an HL7 messaging standard, is the most used health information exchange standard in the United States. HL7 calls V2 the “workhorse of electronic data exchange in the clinical domain” and in 2024 reported that 95% of U.S. healthcare organizations and more than 35 countries were using it (HL7 Version 2 Product Brief).
V2 is used to communicate within and between systems and healthcare organizations. Commonly used message types include those about patient movement (admission, discharge, or transfer), orders (e.g., with laboratories or pharmacies), test results, clinical reports, billing, and scheduling. V2 is also used for public health communications such as reporting results, disease surveillance, and immunization tracking.
Message Profiles
V2 is based on the concept of message profiles. For each type of health information message, its V2 profile specifies the order, structure, and types of data that can be included, including specific spacers or delimiters between message components.
For example, a laboratory result is one type of message between healthcare providers. V2 specifies that any message has specific labeled segments, or sets of fields, corresponding to the message type. Some segments are required, others are optional.
A laboratory result message would be sent as an “Observation Result” message in V2 and might include segments such as the message header, patient identification, patient visit (or interaction), an observation request (or the request for a lab test), and one or more observations (or test results).
The below example is an excerpt of a V2 message reporting on the results of a blood sodium test for a patient named John Doe:
Each segment within a message will have a set of specified fields relevant to that context.
| Segment | Name | Required | Includes | Example |
|---|---|---|---|---|
| MSH | Message Header | R | The organization (e.g., laboratory) sending the message; the message type and standards used. |
MSH|^~\&|LABSYS|HOSP|CLINIC|HOSP|202308311230||ORU^R01|678901|P|2.5
|
| PID | Patient Identification | R | Identification and description of the specific patient. |
PID|1||12345678^^^HOSP^MR||DOE^JOHN^^^^||19800101|M|||123 Main St^^Somewhere^CA^90210
|
| OBR | Observation Request | R | What the doctor ordered, including the laboratory coding system used and the code and description of the test(s). |
OBR|1|67890|54321|2951-2^Sodium [Moles/volume] in Serum or Plasma^LN||202308311200|||Dr. Smith^John
|
| OBX | Observation | The results for one observation (test); the code for the test and the description of the results. |
OBX|1|NM|2951-2^Sodium [Moles/volume] in Serum or Plasma^LN||142|mmol/L|135-145|N|||F
|
When appropriate, other standards like terminology standards are used within the message. In the example above:
- The identifier 2951-2 in the Observation Request (OBR) segment is the unique identifier from LOINC for the test that was ordered (a test for sodium in the blood, i.e., serum sodium).
- The same LOINC identifier 2951-2 in the Observation (OBX) segment shows that the result given is for a serum sodium test.
As discussed in Module 2, using unique identifiers from agreed-upon terminology standards are an important step towards removing ambiguity about which tests are requested and what is being reported.
Activity
Consider the example V2 message below:
V2 Observation Result (ORU) Message (abbreviated for illustration)MSH|^~\&|NIST Test Lab APP|NIST Lab Facility||NIST EHR Facility|20150926140551||ORU^R01^ORU_R01|NIST-LOI_5.0_1.1-NG|T|2.5.1|||AL|AL||||| PID|1||PATID5421^^^NIST MPI^MR||Wilson^Patrice^Natasha^^^^L||19820304|F||2106-3^White^HL70005|144 East 12th Street^^Los Angeles^CA^90012^^H||^PRN^PH^^^203^2290210|||||||||N^Not Hispanic or Latino^HL70189 ORC|NW|ORD448811^NIST EHR|R-511^NIST Lab Filler||||||20120628070100|||5742200012^Radon^Nicholas^^^^^^NPI^L^^^NPI OBR|1|ORD448811^NIST EHR|R-511^NIST Lab Filler|1000^Hepatitis A B C Panel^99USL|||20120628070100|||||||||5742200012^Radon^Nicholas^^^^^^NPI^L^^^NPIOBX|1|CWE|22314-9^Hepatitis A virus IgM Ab [Presence] in Serum^LN^HAVM^Hepatitis A IgM antibodies (IgM anti-HAV)^L^2.52||260385009^Negative (qualifier value)^SCT^NEG^NEGATIVE^L^201509USEd^^Negative (qualifier value)||Negative|N|||F|||20150925|||||201509261400
Can you identify the following information:
What laboratory is sending the message?
What is the patient’s name?
What is the test being ordered?
For more and complete sample messages, see the HL7 Confluence site.
V2 message profiles do not specify how a message is transmitted, nor how it is rendered or displayed. The communicating institutions decide how the message is transmitted, and each individual institution determines how the information is rendered for human users of their system.
Limitations of V2
(Image Source: iStock Photos, kirstypargeter©)
V2 is popular because it is easy to use, understand, and implement. It works well within a single organization, where everyone can agree on what data elements will be exchanged, what terminologies will be used, and when the data will be exchanged. V2 depends on agreements between the participating communicating parties about their implementations. V2 implementations are often highly customized and can require a lot of time and resources to implement with many participating communicating parties.
As we expand health data exchange across institutions, nationally or even globally, it isn’t practical for each organization to create its own custom agreement with every organization it would want to communicate with. Because of this, continual improvement toward interoperability continues.
Implementation Guides
Rather than one required set of message profiles that each user of V2 must implement, organizations can create their own implementation guides that will define the relationships, vocabularies, and processes they use and the message profiles that go along with it. Implementation guides are shared across organizations and platforms to enable institutions to communicate effectively while maintaining compliance and standards.