7 Steps How To Read Health Level Seven (HL7) Messages

(doylc.com) How to Read HL7 Messages - Health Level Seven (HL7) is an interoperability standard used in healthcare. It is the language that health information systems use to communicate. For example, public health departments have immunization registries and syndromic surveillance systems that need to communicate with electronic health record systems (EHRs) in hospitals and clinics. This is achieved with HL7 messaging. Although the HL7 standards have undergone two major revisions since HL7 v2, it still remains the health standard and the version you're most likely to find in this space.

Steps by Steps :

1. Understand the HL7 message structure. Here is a typical HL7 message with syntax highlighting added to make it easier to identify the elements in a message: MSH | ^ ~ & | ADT1 | MCM | LABADT | MCM | 198808181126 | SECURITY | ADT ^ A01 | MSG00001- | P | 2.6 EVN | A01 | 198808181123

PID | | |PATID1234 ^ 5 ^ M11 ^^ A | _ | JONES ^ WILLIAM ^ A ^ III | | 19610615 | M | | 2106-3 | 677 DELAWARE AVENUE ^ ^ EVERETT ^ MA ^ 02149 | GL | (919) 379-1212 | (919)271-3434 ~ (919)277-3114 | | S | | PATID12345001 ^2 ^ M10 ^^ ACSN | _ 123456789 | 9-87654 ^ NC NK1 | 1 | JONES ^ BARBARA ^ K | SPO | | | | | 20011105NK1 | _ 1 | JONES ^ MICHAEL ^ A | FTH PV1 | 1 | i | 2000 ^ 2012 ^ 01 |

| | | 004777 ^ LEBAUER ^ SIDNEY ^ J. | | | Sur
| | - | | Administrator | A0
AL1 | 1 | | ^ PENICILLIN | | CODE16 ~ CODE17 ~ CODE18
AL1 | 2 | | ^ CAT SKIN | | CODE257
DG1 | 001 | I9 | 1550 | MAL NEO LIVER, PRIMARY | 19880501103005 | FPR1 |
_ 2234 | M11| 111 ^ CODE151| COMMON PROCEDURES | 198809081123
ROLL | 45 ^ RECORDER ^ REEL MASTER LIST | AD | RO | KATE ^ SMITH ^ ELLEN | 199505011201
GT1 | 1122 | 1519 | BILL ^ GATES ^ A
IN1 | 001 | A357 | 1234 | BCMD | | | | | 132987
IN2 | ID1551001 | 123456789
ROLL | 45 ^ RECORDER ^ REEL MASTER LIST | AD | RO | KATE ^ ELLEN | 199505011201

Messages are made up of segments, fields, components, and subcomponents. Segments can be thought of as containers grouped like data types. This data is contained in the fields of a segment. The three digit codes in blue are the segment designations for this message.

Each segment contains fields separated by the light blue '|'. Character. Fields and segments can be repeated. Repeating fields are separated with the red character '~'. Components are the data points within fields and are separated by the green character '^'. Subcomponents are separated by the light purple separator '&'. These special characters are called control characters. The table contains the standard control characters used in HL7.

2. Break the message into segments. Segments are the basic structural elements that make up HL7 messages. Each message consists of one or more segments.

The message type determines which segments a message contains, which are optional, and which are repeatable. This syntax is dictated by the HL7 version used when constructing the message. Segments are reusable in different message types.

The segments in the example message are listed in the table:

3. Divide the segments into fields. The following diagram is a conceptual model of an HL7 message divided into segments and fields. The three-digit code at the beginning of each segment serves as identification. Fields are noted by adding the field's index number to the segment. For example, the first field in the message header would be MSH-1, the second field would be MSH-2, and so on.

MSH, the message header, is the first segment in every HL7 message and contains message metadata. The second segment in each message is the EVN segment. This contains the event that triggers the message. In this example, this event is the planning of an inpatient operation.

4. In the sample message, notice that not all fields contain data. The following section of segment NK1 (Next of Kin) contains empty fields. The empty fields here are denoted by field separators (|) with no intervening fields, followed by the date in the format Yymmdd:

SPO | | | | | 20011105

5. Note that repeating fields are separated by the ~ character. This example shows a repeating allergic reaction field (AL1.5[1-3]) in the allergies (AL1) segment:

CODE16 ~ CODE17 ~ CODE18

6. Split the fields into components. Each component in a field is separated by the ^ character. Fields are notated by adding a decimal point to the segment notation followed by the field's index number. For example, the street address component is part of the address field and can be indexed with PID-11.1. PID is the patient identification segment. PID-11.1 is the street address component of the address field (PID-11).

Components can be further broken down into subcomponents using the & character as a separator.

7. Use the HL7 Data Dictionary to look up items. The data dictionary for all elements contained in a message can be found by referencing the standard for the version of HL7 used to compose the message. The version number can be found in the MSH-12 field of any message header.

Appendix A of the standard contains a data dictionary for all elements in a message. It is available in both PDF and XLS file format. The data dictionary for HL7 v2.6 is a case in point.