> ## Documentation Index > Fetch the complete documentation index at: https://mso.getlemma.com/llms.txt > Use this file to discover all available pages before exploring further. # Clinical & billing code sets overview > Orientation to CPT, HCPCS Level II, ICD-10, CDT, NDC, modifiers, and revenue codes: what each does, who maintains it, and the licensing constraints. Orientation table for the code sets that appear on healthcare claims. Each is maintained by a different body, some are licensed, and mixing them up produces denials. **Licensing matters.** CPT is copyrighted and licensed by the AMA; CDT by the ADA. This page describes what each code set is and uses a small number of illustrative codes. It does not reproduce licensed code lists. If you are a healthtech company, you need a commercial license if you want to embed these codes in your product. ## The code sets | Code set | Maintained by | Describes | Where it appears | Licensed? | | ------------------ | ----------------------------------- | --------------------------------------------- | ----------------------- | ----------------- | | **CPT** | American Medical Association | Procedures and services | 837P/I service lines | **Yes, AMA** | | **HCPCS Level II** | CMS | Supplies, drugs, DME, and services not in CPT | 837P/I service lines | No | | **ICD-10-CM** | CDC/NCHS (US clinical modification) | Diagnoses | 837 `HI` segment | No | | **ICD-10-PCS** | CMS | Inpatient hospital procedures | 837I | No | | **CDT** | American Dental Association | Dental procedures | 837D service lines | **Yes, ADA** | | **NDC** | FDA | Drug products | 837 drug identification | No | | **Revenue codes** | NUBC | Facility service categories | 837I | Licensed via NUBC | | **Modifiers** | AMA (CPT) and CMS (HCPCS) | Qualify a procedure | Appended to CPT/HCPCS | Partly licensed | | **POS codes** | CMS | Where the service was delivered | 837 `CLM05` | No | | **Taxonomy codes** | NUCC | Provider type and specialty | 837 `PRV`, NPPES | No | ## CPT Five-character codes for procedures and services, in three categories: | Category | Purpose | | ---------------- | ----------------------------------------------------------------- | | **Category I** | The main set, the five-digit numeric codes used for most services | | **Category II** | Optional performance-measurement tracking codes (`F` suffix) | | **Category III** | Temporary codes for emerging technology (`T` suffix) | Updated annually, effective January 1. **Using a deleted code produces a denial**, so annual code updates are a real operational task. ## HCPCS Level II Alphanumeric codes for items CPT doesn't cover, durable medical equipment, prosthetics, supplies, ambulance services, and drugs administered other than orally. Examples of the letter-series structure: `A` codes for transport and supplies, `J` codes for injectable drugs, `E` codes for durable medical equipment, `G` codes for temporary Medicare procedures. ## ICD-10-CM Diagnosis codes. Three to seven characters, with the structure encoding category, etiology, anatomic site, severity, and in some chapters laterality and encounter type. Updated annually, effective October 1. **Code to the highest level of specificity available.** RARC M81, "you are required to code to the highest level of specificity", is a common denial driver, and unspecified codes are also a medical-necessity vulnerability. If the documentation supports laterality or encounter type, the code should carry it. ## CDT Dental procedure codes, maintained by the ADA. Format is `D` plus four digits, organized by category of service, diagnostic, preventive, restorative, endodontics, periodontics, prosthodontics, oral surgery, orthodontics. 🦷 CDT is a separate licensed code set from CPT, used on 837D claims. A group operating both medical and dental entities needs both, and needs a clearinghouse that handles both formats. See [Dental: the DSO model](/concepts/industries/dental-dsos). ## Modifiers, the common working set Two characters appended to a CPT or HCPCS code to qualify it. | Modifier | Meaning | Notes | | ------------------ | ----------------------------------------------------------------------------------------------------- | ------------------------------------------------------------------------------------ | | **25** | Significant, separately identifiable E/M service by the same physician on the same day as a procedure | **Heavily used and heavily scrutinized** | | **26** | Professional component | Splitting professional from technical | | **TC** | Technical component | | | **50** | Bilateral procedure | | | **51** | Multiple procedures | | | **59** | **Distinct procedural service** | **Enforcement-visible.** Used to bypass NCCI edits; only where clinically justified. | | **XE, XS, XP, XU** | More specific alternatives to 59 | Preferred by CMS where applicable | | **76** | Repeat procedure by the same physician | | | **77** | Repeat procedure by another physician | | | **95** | Synchronous telemedicine via real-time audio and video | | | **GT** | Via interactive audio and video | Legacy; largely superseded by 95 for many payers | | **Q5** | Service furnished under a reciprocal billing arrangement | Narrow rules | | **Q6** | Service furnished under a fee-for-time compensation arrangement | Narrow rules | | **KX** | Requirements specified in the medical policy have been met | **An attestation**, must be documentable | | **GA** | Waiver of liability statement on file (ABN) | Medicare | | **GY** | Statutorily excluded | Medicare | | **GZ** | Expected to be denied as not reasonable and necessary | Medicare | **Modifiers 25, 59, and KX carry the most enforcement attention.** * **25**, routinely appending it to every E/M billed with a procedure is a recognized pattern * **59**, using it to override an NCCI edit without clinical justification is unbundling * **KX**, it is an attestation that policy requirements are met. Appending it without supporting documentation is asserting something you cannot prove See [Billing compliance basics](/concepts/compliance/billing-compliance-basics). ## Revenue codes Four-digit codes on institutional (837I) claims identifying the department or service category, room and board, pharmacy, laboratory, operating room. Maintained by the National Uniform Billing Committee. Awareness-level for most outpatient MSO-PC groups; essential if you operate a facility component. ## NDC National Drug Codes identify drug products. Required on claims for many drugs, particularly by Medicaid programs, and carried alongside the HCPCS J-code with quantity and unit of measure. Format is an 11-digit number in a 5-4-2 configuration, though it appears in other configurations on packaging — converting between them is a common source of claim errors. ## Annual update discipline | Code set | Effective | | -------------------------- | --------- | | **ICD-10-CM** | October 1 | | **CPT and HCPCS Level II** | January 1 | | **CDT** | January 1 | **Deleted codes deny.** Both annual updates are operational tasks: update the EHR's code sets, update charge master entries, update scrubber edits, and re-check any hard-coded code lists in your own tooling. Practices that skip an update spend the following quarter working denials that have a single root cause. ## Where each appears on a claim | Field | Code set | | --------------------- | ---------------------------- | | 837 `HI` segment | ICD-10-CM | | 837P `SV1` | CPT / HCPCS, with modifiers | | 837D `SV3` | CDT | | 837I `SV2` | Revenue codes plus CPT/HCPCS | | 837 `CLM05` composite | Place of service | | 837 `PRV` | Taxonomy | | 837 drug loop | NDC | ## Related topics - [The life of a claim](/concepts/payments/claim-lifecycle.md) - [The 837: how claims are told to payers](/concepts/payments/understanding-837s.md) - [Billing compliance: the lines you never cross](/concepts/compliance/billing-compliance-basics.md) - [Submit clean claims](/guides/billing/submit-clean-claims.md) - [Place of service codes](/reference/edi/place-of-service-codes.md) - [Provider taxonomy codes](/reference/edi/taxonomy-codes.md) - [837 file anatomy](/reference/edi/837-anatomy.md)