Question and request raised by Paul Swarts:

I have a question on how to combine CPT codes a FHIR ServiceRequest for the CDS Hooks order-select protocol

For a Diagnostic order 'CT Hip Arthrogram' are two CPT codes needed 73701 (CT Lower Extremity With Contrast), 27093 (Injection Procedure Hip Arthrogram) in our organization this procedure is has also a combined code "CT Hip Arthrogram"

In the FHIR ServiceRequest we want to put both our internal combined-code and the CPT codes.

[...]

Response from the AMA via coreysmith:

Ok..just spoke with one of the AMA's CPT coding experts...here goes:

1. The specific codes 73701+27093 can be combined per the rules in CPT and as specified by the NCCI code edits.
2. There is not a specified grammar in CPT, like in SNOMED, for how codes can and can't be combined based on a defined concept model.
3. CPT does provide guidance on when codes can and can't be combined from a clinical perspective. For example, if there is a code for a Tonselectomy, CPT woud tell you not to combine that code with Incision prpcedure because an incision is included in the scope of the Tonselectomy code. These rules are called "parentheticals" and appear in the CPT book and can also be found in a machine processable version of CPT called CPT Link.
4. Each payer organization will also specify, per there payment policies, when codes can and can't be combined. This is independent of CPT. In the case of CMS, these "code edits" are defined by the National Correct Coding Initiative Edits https://www.cms.gov/Medicare/Coding/NationalCorrectCodInitEd

See Zulip Combine CPT codes discussion for further details.

Based on the above, we should define a syntax in FHIR for the use of CPT codes in combination (consistent with the CPT coding manual and to the extent possible with how this is being done in current standard practice), and we should document that syntax in the Using CPT with FHIR page.

We can do something similar to (but likely simpler than) what has been done for Multiple Coding in ICD-[X].

The expression syntax for use of CPT codes in combination likely should be a string with the multiple codes listed and the individual codes separated by a single space character.  If there is a priority ranking of the codes (which seems likely is not the case from the discussion so far), then the codes should be listed in the order of priority with the highest priority code first.  And we need to decide if a legitimate combination CPT code expression may contain a maximum of two CPT codes, or if more may be allowed.  If it is legitimate in some cases to use more than two CPT codes in combination, then we need to determine what the maximum number of codes that can be combined is (if a specific limit exists).