LOINC codes are never reused or deleted, and the concept meaning is persistent over time despite the fact that there may be modifications to the name (as described above). If we discover that a LOINC term’s meaning is a duplicate of another existing term or it is somehow erroneous, it will be given a Status of DEPRECATED but not removed from the database.
In the past, when we encountered duplicate terms (i.e. terms that had different names but meant the same thing), our general policy was to deprecate the newest term. Many times, this convention worked well because the older term was more likely to have been incorporated into user’s systems through mappings, etc. However, this was not always the case. Sometimes, the new term had the clearer, more recognizable label and thus it was most likely the most mapped-to term. Therefore, our current policy is to make the change to require (in our estimation) the least amount of re-mapping for existing users.
Our general policy is not to make any edits to a term once it is DEPRECATED. However, in rare cases we may update one or more names of DEPRECATED terms in order for them to correctly represent the original meaning of the term. For example, in LOINC 2.66, the Long Common Name for 26693-2, which has the Component Streptococcus pneumoniae 12f Ab, was updated from Deprecated Streptococcus pneumoniae 12 Ab [Mass/volume] in Serum to Deprecated Streptococcus pneumoniae 12f Ab [Mass/volume] in Serum.