Is there a LOINC-CPT mapping available?
Yes and no. The National Library of Medicine sponsored a LOINC-CPT mapping that was performed by Intermountain Health Care and reviewed by Regenstrief and the AMA in 2005-06. That effort mapped terms from LOINC version 2.15 to the 2005 version of CPT and covered many, but not all, of the common laboratory tests. The original intent was to periodically update and expand the LOINC-CPT mappings, but due to funding and other resource issues, the project did not continue.
The basic use-case for the original mapping effort was that LOINC codes would be used for ordering/reporting tests and observations, and the associated CPT codes would be used for billing; thus, this was a unidirectional map from LOINC codes for orders/results to CPT billing codes. The mapping table and more information about the process and mapping assumptions that were made are available through NLM's UMLS website.