> ## Documentation Index > Fetch the complete documentation index at: https://docs.haau3.com/llms.txt > Use this file to discover all available pages before exploring further. # Code systems > The code systems the haau3 Terminology API answers about (LOINC and RxNorm today), with each one's FHIR URI, the names and OIDs it is recognised by, its publisher and its licence. The [Terminology service](https://docs.haau3.com/terminology/terminology-service.md) answers FHIR R4 terminology operations (`CodeSystem/$lookup`, `CodeSystem/$validate-code`, `ValueSet/$expand` and `ValueSet/$validate-code`) about the code systems on this page. Each section says what the system is, who publishes it, the URI to send as `system`, the other names and OIDs a request may use for it, its licence, and whether it is served. | Code system | URI | Status | | - | - | - | | [LOINC](#loinc) | `http://loinc.org` | Served | | [RxNorm](#rxnorm) | `http://www.nlm.nih.gov/research/umls/rxnorm` | Served | | [SNOMED CT](#snomed-ct) | `http://snomed.info/sct` | Not served | | [CPT](#cpt) | `http://www.ama-assn.org/go/cpt` | Not served | | [ICD-10-CM](#icd-10-cm) | `http://hl7.org/fhir/sid/icd-10-cm` | Not served | | [UCUM](#ucum) | `http://unitsofmeasure.org` | Not served | ## LOINC LOINC (Logical Observation Identifiers Names and Codes) identifies laboratory tests, clinical measurements and other observations, and the panels and survey instruments built from them. It is the default here: an operation that names no `system`, or no `url`, asks about LOINC. * **Status:** Served. Available to any caller with an API key. * **URI:** `http://loinc.org` * **Also recognised as:** `LOINC`, `loinc`, `urn:oid:2.16.840.1.113883.6.1` * **Publisher:** Regenstrief Institute * **Licence:** Free to use under LOINC's licence. The notice is in the Terminology service page's [Legal](https://docs.haau3.com/terminology/terminology-service.md#legal) section. * **More:** [Look up a code](https://docs.haau3.com/terminology/terminology-service.md#look-up-a-code) ## RxNorm RxNorm gives the clinical drugs available in the United States normalized names and codes (RxCUIs), and links them to the drug vocabularies used in pharmacy and drug interaction software. * **Status:** Served. Available to any caller with an API key. Held at a named release: `GET /v1/fhir/r4/metadata?mode=terminology` names the release being served, and a deployment with no release published yet answers `503`. * **URI:** `http://www.nlm.nih.gov/research/umls/rxnorm` * **Also recognised as:** `RXNORM`, `RxNorm`, `urn:oid:2.16.840.1.113883.6.88` * **Publisher:** U.S. National Library of Medicine (NLM) * **Licence:** Publicly available from NLM. The notice is in the Terminology service page's [Legal](https://docs.haau3.com/terminology/terminology-service.md#legal) section. * **More:** [RxNorm on the Terminology service page](https://docs.haau3.com/terminology/terminology-service.md#rxnorm): what we hold, and what a "no" means ## SNOMED CT SNOMED CT is a clinical terminology for findings, disorders, procedures, body structures, organisms, substances and more, used in health records worldwide. * **Status:** Not served. SNOMED CT is free in the United States only through a UMLS Metathesaurus licence, and NLM does not permit a vendor to cover its customers under its own licence, so the terminology operations do not serve it. Callers holding their own UMLS credentials will be able to use them here. * **URI:** `http://snomed.info/sct` * **Also recognised as:** `SNOMED`, `SNOMEDCT`, `SCT`, `urn:oid:2.16.840.1.113883.6.96` * **Publisher:** SNOMED International; in the United States, the National Library of Medicine distributes it through the UMLS * **Licence:** Free in the United States through a UMLS licence, which each user holds for themselves. ## CPT CPT (Current Procedural Terminology) codes the medical, surgical and diagnostic services and procedures clinicians report, most often on claims. * **Status:** Not served. CPT is licensed by the American Medical Association and requires a paid distributor licence per product. haau3 does not hold one, so this service will not answer about CPT codes at all. * **URI:** `http://www.ama-assn.org/go/cpt` * **Also recognised as:** `CPT`, `urn:oid:2.16.840.1.113883.6.12` * **Publisher:** American Medical Association (AMA) * **Licence:** Licensed by the AMA, product by product. ## ICD-10-CM ICD-10-CM is the United States' clinical modification of the World Health Organization's ICD-10: the diagnosis codes US claims carry and medical records use for conditions and the reasons for a visit. A new release takes effect each October 1. * **Status:** Not served. ICD-10-CM is public domain and carries no licence restriction, but this service does not yet have a source configured for it. * **URI:** `http://hl7.org/fhir/sid/icd-10-cm` * **Also recognised as:** `ICD10CM`, `ICD-10-CM`, `urn:oid:2.16.840.1.113883.6.90` * **Publisher:** National Center for Health Statistics (NCHS), part of the CDC, under the World Health Organization's authorization * **Licence:** Free to use, with no licence to sign. ## UCUM UCUM (the Unified Code for Units of Measure) is the code system for units of measure that FHIR's `Quantity` uses, such as `mg`, `mL` and `mm[Hg]`. * **Status:** Not served. UCUM is a grammar rather than a list of codes, so it is validated by a unit parser rather than looked up on a terminology server. A lookup endpoint is the wrong shape for the question. * **URI:** `http://unitsofmeasure.org` * **Also recognised as:** `UCUM`, `urn:oid:2.16.840.1.113883.6.8` * **Publisher:** Regenstrief Institute * **Licence:** Free to use under Regenstrief's UCUM terms. ## A system that is not listed A request naming a system that is not served comes back as a FHIR `OperationOutcome` with an issue code of `not-supported`, saying which kind of no it is: a system nobody publishes, a system we are not licensed to serve, or one that needs a licence you hold rather than one we can pass on. The service does not guess. Systems that are not listed at all are also answered rather than errored. Most real-world coded data carries site-specific systems that no terminology server can resolve, so an honest "I do not recognise this" is a normal answer here, not a failure. This page is the service's intent, generated from its registry so it cannot drift from the code. What a particular deployment is answering right now, including which release it holds of a code system it keeps itself, comes from `GET /v1/fhir/r4/metadata?mode=terminology`. This documentation is built and hosted on [Mintlify](https://mintlify.com), a developer documentation platform.