LOINC development follows best practices for terminology system development by never reusing or deleting codes. If a LOINC term is identified as erroneous or a duplicate of a previous term it is flagged as deprecated in the database, but the record is not removed. Changes in concept status are made very judiciously.
Prior to the LOINC version 2.31 release (June 2010), we identified such deprecated terms by populating the STATUS field of the database with DEL and wherever possible identified superseding concepts in the MAP_TO field of the LOINC Table. Active (non-deprecated) records had no value (null) in the STATUS field. Based on new use cases and input from the LOINC community, LOINC 2.31 implemented an expansion to that classification. The presently supported values for term Status, with the definition and implications for use, are:
| Status | Description |
|---|---|
| ACTIVE | Concept is active. Use at will. |
| TRIAL | Concept is experimental in nature. Use with caution as the concept and associated attributes may change. |
| DISCOURAGED | Concept is not recommended for current use. New mappings to this concept are discouraged; although existing mappings may continue to be valid in context. Wherever possible, the superseding concept is indicated in the MAP_TO field of the MapTo Table (see Appendix A) and should be used instead. |
| DEPRECATED | Concept is deprecated. Concept should not be used, but it is retained in LOINC for historical purposes. Wherever possible, the superseding concept is indicated in the MAP_TO field of the MapTo Table (see Appendix A) and should be used both for new mappings and updating existing implementations. |
Furthermore, LOINC 2.31 added two new fields:
| Status | Description |
|---|---|
| STATUS_REASON | Classification of the reason for concept status. This field will be Null for ACTIVE concepts, and optionally populated for terms in other statuses where the reason is clear. DEPRECATED or DISCOURAGED terms may take values of: AMBIGUOUS, DUPLICATE, or ERRONEOUS. |
| STATUS_TEXT | Explanation of concept status in narrative text. This field will be Null for ACTIVE concepts, and optionally populated for terms in other statuses. |
Our initial implementation of these new concept status values in LOINC 2.31 populated the STATUS field with ACTIVE or DEPRECATED based on their existing status and have identified a limited set of terms that have been designated DISCOURAGED or TRIAL.
The principal reason identifying terms as DISCOURAGED is where we have strong inclinations that a particular term is no longer valid given current practice. For example, we have flagged as DISCOURAGED several lutropin terms with Properties consistent with mass or molar units because all lutropin sources that we could reach report concentrations in international units (IU) per volume and the drug lutropin is prescribed in terms of international units per volume. To avoid confusion on the part of mappers, the DISCOURAGED Status steers them away from these terms to the more likely candidates.
The principal reason for identifying terms as TRIAL is a very constrained circumstance, such as when the source of the term is still equivocating. This has been illustrated in our work to create a LOINC representation of federally-required patient assessment instruments. Here, the item meaning is defined in the context of use within that instrument. We have been fortunate to work with assessment developers in the early stages of instrument development. This is advantageous because it enables the codes to be included in data specifications and documents as they are developed, but we are in the position of creating codes and names for data elements whose attributes are still in flux. As the instrument evolves, the specific representation of the item (question) or answer options on the form may change. Ultimately, the representation will be settled by an authoritative body (such as CMS) and they are intended for use in one context – the official release of the instrument. Identifying these terms as TRIAL allows us to include them in the public distribution while clearly flagging their “pending” status. Once the final concept representation has been determined, terms initially labeled TRIAL would be reclassified as ACTIVE (or perhaps in rare circumstances DEPRECATED or even rarer DISCOURAGED).
In LOINC 2.42, the MAP_TO field of the LOINC Table was removed and replaced with a separate MapTo table. The original MAP_TO field was created to store a single replacement LOINC term number for when a LOINC was deprecated. We later learned that there were times when there was more than one possible replacement term, depending on certain conditions. To address this problem we created a new MapTo table that was first released with version 2.34. The original MAP_TO field was retained for a few releases, but was removed from the LOINC Table in version 2.42. See Appendix A for information about the MapTo table.
In rare cases, we have had to “undeprecate” DEPRECATED terms when upon further, very careful review, we discovered that the concepts are, in fact, valid. Such terms will revert back to a STATUS of ACTIVE but can be identified by the value UNDEL in the Chng_Type field. We have chosen to undeprecate the codes in such rare cases (instead of making new terms) because DEPRECATED terms continue to be included in the LOINC database, and some users may continue to use such concepts or have historical data associated with those codes. If we were to create new codes for the same concept, different users could potentially use different codes to identify the exact same data.
Special use code deprecation
Several codes made available as part of our Special Use process prior to version 2.83 were mistakenly not included in the 2.83 release because they were changed to a Deprecated status. We have since established a policy to deem Special Use codes as “published” even if they are changed to Deprecated. Therefore the omitted codes will be published with version 2.84 along with MAP_TO values.