PHER-CR06-ELR IG CE vs C Issue

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Submitted by: Austin Kreisler on behalf of Riki Merrick	Revision date: <<Revision Date>>
Submitted date: 2/1/2011	Change request ID: CR-06
Standard: ELR IG	Artifact ID, Name: ELR IG

Issue

Defintions for C and CE: C – Conditional. HL7 Definition: This usage has an associated condition predicate (See section 2.B.7.6, "Condition predicate"). If the predicate is satisfied: A conformant sending application must always send the element. A conformant receiving application must process or ignore data in the element. It may raise an error if the element is not present. If the predicate is NOT satisfied: A conformant sending application must NOT send the element. A conformant receiving application must NOT raise an error if the condition predicate is false and the element is not present, though it may raise an error if the element IS present.

CE – Conditional, but may be empty. HL7 Definition: This usage has an associated condition predicate (See section 2.B.7.6, "Condition predicate"). If the predicate is satisfied: If the conforming sending application knows the required values for the element, then the application must send the element. If the conforming sending application does not know the values required for this element, then the element shall be omitted. The conforming sending application must be capable of knowing the element (when the predicate is true) for all 'CE' elements. If the element is present, the conformant receiving application shall process (display/print/archive/etc.) or ignore the values of that element. If the element is not present, the conformant receiving application shall not raise an error due to the presence or absence of the element. If the predicate is not satisfied: The conformant sending application shall not populate the element. The conformant receiving application may raise an application error if the element is present.

So the only certain statement one can make for CE is, when it should not be populated, namely when the condition is not met. When the condtion is met and no data is sent, one cannot distinguish between an application that does not have data for this instance from an application that does not support the element, unless you have used test data that provides data for teh CE defined fields, so that it can be sent.

We examined the use of CE in more detail in the CWE datatype: Use of CE in CWE.3 and CWE.6 would essentially allow a code to be sent without a coding sytem identifier, which introduces ambiguity. For CWE.2 and CWE.4 the condition seems to be indicating, that it would never be populated, as the conditon is written so when it is met the field needs to be empty and per definition above when the condition is not met, it cannot be populated.

Use of CE for CWE.9 was intended to provide for at least the text to be sent, if no codes were available at all from a sender (no standard nor local codes). The condition for CWE.9 makes that clear: Either original Text is used to convey the text that was the basis for coding, or when there is no code to be sent, only free text. ELR Condition predicate: If no identifier and alternate identifier are present, then this component is required.

Recommendation

• Suggestion is to change CE to C in the case of CWE and examine use of CE in all other instances as well.

Resolution

Considered for future use (ELR Release 2) and provided guidance "It is recommended that CWE.9 have a usage code of C (Conditional) with conditional rule that that CWE.9 must be populated if nothing else in the datatype is populated." as part of ELR r1 Errata.