Why does a snomed term contain two codes?
I understand that a term is only denoted by one code
eg: headache
One of them is invalid and non-standard. So it’s not used currently
Exactly as @Mikita_Salavei says: The source codes are given to us by the source vocabularies. We have no control over that. Our concepts on the other hand that we derive from these source codes will make sure only one of them is standard, and the other one is not.
thank you 
helps me a lot
@Mikita_Salavei Thanks for helping out. Sometimes I do see both SNOMED codes are standard and valid and linked to the same SNOMED term. Would it be possible to update these rare terms in future? Thanks!
4120320 302896008 Keratoconjunctivitis sicca
Clinical Finding Standard Valid Condition SNOMED
4103749 193776001 Keratoconjunctivitis sicca
Clinical Finding Standard Valid Condition SNOMED
It’s not the same codes. Code 4120320 302896008 Keratoconjunctivitis sicca
Clinical Finding Standard Valid Condition SNOMED subsumes code 4103749 193776001 Keratoconjunctivitis sicca ( excluding Sjögren syndrome) Clinical Finding Standard Valid Condition SNOMED. The meaning of first code is more wide. But actually sometime may be possible coexistance of two similar codes in one vocabulary.
Right! And we try not to interfere because the SNOMED is doing the cleanup job by themselves. It would be useful to report any issues to SNOMED. Also, we’re collecting the bugs and report to SNOMED in bulks.
@Alexdavv @Mikita_Salavei Thanks so much for the information! Now I found some better examples but I am not sure whether these terms have been corrected. The previous example was generated by using old version of OMOP concept data. How can I tell whether we have the newest concept file for our OMOP data?
Concept Id Concept Code Concept Name Domain Standard Concept
4189647 414850009 Neutrophilia Condition Standard
4306106 165518003 Neutrophilia Condition Standard
46269998 112401000119106 Lesion of conjunctiva Condition Standard
762773 431651000124109 Lesion of conjunctiva Condition Standard
76744 48188009 Azoospermia Condition Standard
4143116 425558002 Azoospermia Condition Standard