Pattern to identify LOINC codes, derived from the description in LOINC.org (June 2024):-

LOINC codes have a fixed length field of 7 characters within the LOINC database. Current codes are from 3-7 characters long. If you are currently building a system to include LOINC codes, we advise allowing up to 10 characters (or at least 8 characters) to allow for further expansion. When the LOINC database contains 100,000 different LOINC records, the fixed length field will need to expand to 8 characters. The last digit of the LOINC code is a check digit and is always preceded by a hyphen (dash). The hyphen, as well as all the numbers, is part of the LOINC and must be included. The check digit is always a number form 0-9 and serves to help avoid errors in transcription of the code. Current licensing agreement for use of LOINC codes requires you to send the complete LOINC code.