When expressions are used to record clinical data, it is important to establish effective ways of communicating these expressions with other systems.

The main options for sharing postcoordinated expressions are:

• To exchange the terse expression as the ‘code’ of the relevant field, with the displayed or auto-generated term.
  • For example, the HL7 version 3 CD data type (Release 2) allows the 'code' property to include SNOMED CT expressions (see HL7 TermInfo guide).
  • Within the coding also include a precoordinated concept, for systems that can not process expressions. This should be the proximal inferred parent concept of the expression.
  • This option is shown in the example below.
• To decompose the expression into separate fields - one for a focus concept and then one for each of the attribute values in the expression.
  • In each field, the concept identifier may be used as the code, and one of the synonyms as the display text.
  • This approach assumes alignment between the message structure and the relevant parts of the SNOMED CT concept model.
• To use an expression identifier from your expression repository as the ‘code’, with the display term.
  • This approach requires the use of a shared expression repository enabling the recipient system to look up and resolve this identified to the relevant expression.
    

{
  "resourceType": "Condition",
  "id": "f205",
  "text": {
    "status": "generated",
    "div": "<div xmlns=\"http://www.w3.org/1999/xhtml\">...</div>"
  },
  "clinicalStatus": {},
  "verificationStatus": {},
  "code": {
    "coding": [
       {
        "system": "http://snomed.info/sct",
        "code": "301354004 |Pain of ear| : 272741003 |Laterality| = 7771000 |Left|",
        "display": "Left ear pain"
      },
      {
        "system": "http://snomed.info/sct",
        "code": "301354004 |Pain of ear|",
        "display": "Pain of ear"
      }
    ]
  },
  "subject": {
    "reference": "Patient/f201",
    "display": "PP"
  },
  "recordedDate": "2013-04-04",
  "asserter": {
    "reference": "Practitioner/f201"
  }
}