Specifies a coded element and its associated detail. The CWE data type is used when 1) more than one table may be applicable or 2) the specified HL7 or externally defined table may be extended with local values or 3) when text is in place, the code may be omitted.

Usage Notes: This is a field that is generally sent using a code, but where the code may be omitted in exceptional instances or by site agreement. Exceptional instances arise when the coding system being used does not have a code to describe the concept in the text.

Components 1-3 & 7 are used in one of three ways:

1. Coded: The identifier contains a valid code from a coding system. The coding system must either be present and have a value from the set of allowed coding systems, or if not present, it will be interpreted to have the same meaning as if it had been valued with the code meaning "HL7 coding system". Refer to HL7 Table 0396 in section 2.17.5 for valid values. The table includes ASTM E1238-94, Diagnostic, procedure, observation, drug ID, and health outcomes coding systems. If the coding system is any system other than "HL7 coding system," version ID must be valued with an actual version ID. If the coding system is "HL7 coding system," version ID may have an actual value or it may be absent. If version ID is absent, it will be interpreted to have the same value as the HL7 version number in the message header. Text description is optional, but its use should be encouraged to aid in readability of the message during testing and debugging.

   Example 1a: OBX segment where the observation identifier is a LOINC code and the observation value is being sent as a CWE value, and the value is taken from SNOMED International.

   OBX|1|CWE|883-9^ABO Group^LN|1|F-D1250^Type O^SNM3^^^^3.4|||N||F<cr>

   Example 1b: OBX segment where the observation identifier is a LOINC code and the observation value is being sent as an CWE value, and the value is taken from a (currently hypothetical) HL7 table.

   OBX|1|CWE|883-9^ABO Group^LN|1|O^Type O^HL74875^^^^2.3.1|||N||F<cr>

2. Uncoded: Text is valued, the identifier has no value, and coding system and version ID follow the same rules as discussed for option 1.

   Example 2: OBX segment where the observation identifier is a LOINC code and the observation value is being sent as a CWE value, and the value is sent as text because the correct clinical value, "Wesnerian" was not found in the set of allowed values.

   OBX|1|CWE|883-9^ABO Group^LN|1|^Wesnerian^SNM3^^^^3.4|||A||F<cr>

3. Data missing: The name of the coding system is "HL7 CWE Status," version ID is either a real version, or if not present it has the same meaning as the version in the message header, and the identifier takes its value from one of the allowed CWE field statuses. The codes for the allowed CWE field statuses are shown below and will be maintained in a table as part of the HL7 vocabulary. Text description of code is optional.

   Example 3: OBX segment where the observation identifier is a LOINC code and the observation value is being sent as an LCE value, and no value can be sent because the test was not done.

   OBX|1|CWE|883-9^ABO Group^LN|1|NAV^Not Available^HL70353^^^^2.3.1|||N||F<cr>

Component 9:

This is the original text that was available to an automated process or a human before a specific code was assigned. This field is optional.

Components 3-6 & 8:

Components 3-6 & 8 are optional. They are used to represent the local or user seen code. If present, components 3-6 & 8 obey the same rules of use and interpretation as described for components 1-3 & 7 (of the CWE data type). If both are present, the identifiers in component 4 and component 1 should have exactly the same meaning; i.e. they should be exact synonyms.

Example 4: OBX segment where the observation identifier is a LOINC code and the observation value is being sent as an CWE value, and the value is taken from SNOMED International. The user seen fields are being used to represent a local coding system (99LAB) used in the sending system.

OBX|1|CWE|883-9^ABO Group^LN|1|F-D1250^Type O^SNM3^O^O Type Blood^99LAB^3.4^|||||F<cr>

Summary of CWE usage notes with table of status values for various states without values:

The CWE data type should be used for coded fields that are optional or where it is permissible to send text for items that are not yet a part of the approved value set. In the normal situation, the identifier is valued with the code from the value set. If the value of the field is known, but is not part of the value set, then the value is sent as text, and the identifier has no value. If the field has an unknown status, then third form of the field is used (see Data missing above), and the appropriate status for the field is selected from the table of allowed statuses. When no code exists, refer to HL7 Table 0353 – CWE statuses for valid values.

Where a text modifier might accompany a code, the "field" in the HL7 message would be of data type CWE and would be allowed to repeat. The first instance of the field would be used, as per option 1; i.e. the identifier would have a valid code. The second instance of the repeating field would be used, as per option 2, that is, the text description would take the value of the free text modifier.