We don't need a separate element/extension because modifiers can (and should) be sent as part of the CPT code.  There is an existing syntax of {CPT code}-{modifier}... that can be used. However, this isn't yet described on the [Using CPT] ( https://terminology.hl7.org/CPT.html) page on THO.  We will submit a request to update that page to include guidance on the post-coordination syntax. We will also add a note in CRD in the place where we talk about use of CPT codes that points to that page and note that modifiers can be sent in a post-coordinated manner. We will also raise a change request for PAS that it should clarify whether CPT post-coordination is allowed in Claim or not.