In the HL7 OID registry (http://www.hl7.org/oid/index.cfm), there is an OID defined for LOINC: 2.16.840.1.113883.6.1 (although curiously there appears to be another candidate there too: 2.16.840.1.113883.11.16492).
My question is, how are different versions of LOINC code sets represented? If there is a single OID to identify LOINC, something else in an HL7 message must convey the version. Alternately, perhaps there are several OIDs, one for each version of the LOINC?
The HL7 OID ending with …6.1 is appropriate when using LOINC codes in HL7 messages and documents. I don’t know about the other OID, and had not seen it before your post.
As far as I know, there is no versioning of LOINC codes. RELMA is versioned, and the LOINC database as a full distribution is versioned; however, the individual LOINC codes are not versioned. Once a code is assigned to a concept, the code always represents that concept (although the code may be deprecated in favor of some other LOINC code when duplicate concepts are found).
So just to be absolultely clear, I think you’re saying that there is a single OID for LOINC regardless of the LOINC release version (e.g 2.24, 2.21). How would a receiving system know to which LOINC version the LOINC codes conveyed in the message belong?