HL7

From FreemedDeveloperWiki, the FreeMED developers' Wiki.

HL7 stands for Health Level 7, and is one of the predominant interface formats for medical record information. The currently used implementation is version 2.3, though there have been plans to migrate to an XML-based variant (version 3).

Contents 1 Import 1.1 Importing from outside FreeMED 1.2 Supported Messages 1.3 Creating an additional message handler 2 Export

Import

Import of HL7 messages is handled by FreeMED.Parser_HL7v2. This is called like this:

 $hl7 = CreateObject('_FreeMED.Parser_HL7v2', $message);
 $hl7->Handle();

Note the use of the _FreeMED namespace, which is safe in any context, be it XML-RPC or standard FreeMED context.

The Parser_HL7v2 class calls FreeMED.Handler_HL7v2 which then calls FreeMED.Handler_HL7v2_(messagetype) depending on the message which is being parsed. If there is no handler, it will log to syslog and exit gracefully.

Importing from outside FreeMED

There is an XML-RPC call, FreeMED.Transport.parse, which allows data to be pulled in from outside the system. It is used like this:

 FreeMED.Transport.parse('HL7v2', message)

There is also a "bridge" which allows an HL7-compliant socket to be set up to relay messages into the system this way. It is in the Subversion repository as hl7_bridge.

Supported Messages

• ADT A04 - Addition of patient record information
• ADT A08 - Modification of patient record information
• SIU S12 - Addition of scheduling information
• SIU S15 - Deletion of scheduling information
• ORU R01 - Observation results message/unsolicited (lab results)

Creating an additional message handler

 <?php
         // $Id: class.Handler_HL7v2_A04.php 1956 2005-03-19 17:49:17Z rufustfirefly $
         // $Author: rufustfirefly $
 
 LoadObjectDependency('_FreeMED.Handler_HL7v2');
 
 class Handler_HL7v2_A04 extends Handler_HL7v2 {
 
         function Handle () {
                 syslog(LOG_INFO, 'HL7 parser| Entered A04 parser');
                 if (!is_object($this->parser)) {
                         die('Handler_HL7v2_A04: parser object not present');
                 }
 
                 .
                 .
                 .
 
         } // end method Handle
 
         function Type () { return 'ADT'; }
 
 } // end class Handler_HL7v2_A04
 
 ?>

The Parser_HL7v2 class parses the HL7 message in the following way:

• $this->message[segment][index] - Parsed segments. This will be an array of arrays, and contains the actual HL7 data.
• $this->map[absolute_position]['type'] - Used for mapping the segment at the specified absolute position to a segment type.
• $this->map[absolute_position]['position'] - Used for mapping the segment at the specified absolute position to an element in the $this->message[] hash.

To retrieve the segment at absolute position x, you could use:

 $segment = $this->message[$this->map[x]['type']][$this->map[x]['position']];

Export

To export messages (generate HL7 messages when certain triggering events occur in the system), the easiest method would be to use Breakpoints and Handlers to generate an HL7 event upon a corresponding event in the system.