> ## Documentation Index
> Fetch the complete documentation index at: https://docs.connectivehealth.io/llms.txt
> Use this file to discover all available pages before exploring further.
# Code Systems
> How Connective Health codes are represented as FHIR Codings
# Overview
Nearly every clinical field in a Connective Health FHIR output is a
[Coding](https://www.hl7.org/fhir/R4/datatypes.html#Coding) with three parts:
| Coding element | Source |
| -------------- | ------------------------------------------------------------------------------------------------------------------------------------------------------------ |
| `system` | The canonical FHIR URI for the terminology the code came from -- resolved from the source code system identifier, see [Code system URIs](#code-system-uris). |
| `code` | The code value, normalized as described under [Code normalization](#code-normalization). |
| `display` | The human-readable description that accompanied the code in the source data. |
`display` is the description **as the source provided it**, not a lookup from the terminology. It may differ in
wording or casing from the terminology's official display for that code.
# Code system URIs
Source data identifies terminologies by OID. Each is published as its registered canonical FHIR URI where one exists,
and as a `urn:oid:` URN where it does not.
| Terminology | OID | FHIR `system` |
| -------------------------------------- | ---------------------------------- | ------------------------------------------------------ |
| LOINC | `2.16.840.1.113883.6.1` | `http://loinc.org` |
| SNOMED CT | `2.16.840.1.113883.6.96` | `http://snomed.info/sct` |
| RxNorm | `2.16.840.1.113883.6.88` | `http://www.nlm.nih.gov/research/umls/rxnorm` |
| CVX | `2.16.840.1.113883.12.292` | `http://hl7.org/fhir/sid/cvx` |
| NDC | `2.16.840.1.113883.6.69` | `http://hl7.org/fhir/sid/ndc` |
| CPT | `2.16.840.1.113883.6.12` | `http://www.ama-assn.org/go/cpt` |
| ICD-9-CM Diagnosis | `2.16.840.1.113883.6.103` | `http://hl7.org/fhir/sid/icd-9-cm` |
| ICD-9-CM Procedure | `2.16.840.1.113883.6.104` | `http://hl7.org/fhir/sid/icd-9-cm` |
| ICD-9 (International) | `2.16.840.1.113883.6.42` | `http://hl7.org/fhir/sid/icd-9` |
| ICD-10-CM Diagnosis | `2.16.840.1.113883.6.90` | `http://hl7.org/fhir/sid/icd-10-cm` |
| ICD-10-PCS Procedure | `2.16.840.1.113883.6.4` | `http://hl7.org/fhir/sid/icd-10-pcs` |
| HL7 Act Code | `2.16.840.1.113883.5.4` | `http://terminology.hl7.org/CodeSystem/v3-ActCode` |
| NUCC Provider Taxonomy | `2.16.840.1.113883.6.101` | `http://nucc.org/provider-taxonomy` |
| CCS | `2.16.840.1.113883.6.115` | `urn:oid:2.16.840.1.113883.6.115` |
| HL7 Administrative Gender | `2.16.840.1.113883.5.1` | `urn:oid:2.16.840.1.113883.5.1` |
| CDT | `2.16.840.1.113883.6.13` | `urn:oid:2.16.840.1.113883.6.13` |
| HCPCS | `2.16.840.1.113883.6.285` | `urn:oid:2.16.840.1.113883.6.285` |
| MED-RT | `2.16.840.1.113883.6.345` | `urn:oid:2.16.840.1.113883.6.345` |
| Source of Payment Typology | `2.16.840.1.113883.3.221.5` | `urn:oid:2.16.840.1.113883.3.221.5` |
| NCI Thesaurus | `2.16.840.1.113883.3.26.1.1` | `urn:oid:2.16.840.1.113883.3.26.1.1` |
| NDF-RT | `2.16.840.1.113883.3.26.1.5` | `urn:oid:2.16.840.1.113883.3.26.1.5` |
| CDCREC (Race and Ethnicity) | `2.16.840.1.113883.6.238` | `urn:oid:2.16.840.1.113883.6.238` |
| Connective Health Panel Classification | `2.16.840.1.113883.3.9359.3.300.1` | `http://connectivehealth.io/fhir/panel-classification` |
ICD-9 (International) and ICD-10-PCS Procedure are distinct terminologies from ICD-9-CM and ICD-10-CM
Diagnosis above -- they use different OIDs. ICD-9 (International) is actively checked when resolving an
[Encounter](/fhir/resources/encounter) diagnosis code. ICD-10-PCS Procedure is mapped defensively for
completeness even though no current source field is known to carry that OID; if one ever does, it will now
resolve to its correct FHIR URI rather than falling back to `urn:oid:`.
## Fallback behavior
| Source code system value | Published `system` |
| ------------------------------------------------------ | ------------------------------------------------------------------------------ |
| An OID in the table above | Its mapped FHIR URI. |
| Any other OID | `urn:oid:{oid}` -- valid FHIR, but not a recognized canonical terminology URI. |
| A value that is already an `http://` or `https://` URI | Passed through unchanged. |
| Absent | No `system` is published on the coding. |
Codings under a `urn:oid:` system are still conformant FHIR, but consumers doing terminology validation should
expect not to resolve them against a published code system.
## Connective Health Panel Classification
`http://connectivehealth.io/fhir/panel-classification` is a **Connective Health terminology**, not a standard one. It
groups laboratory and diagnostic results into clinically meaningful panels, and is published as an *additional* coding
alongside the result's own standard coding -- never as a replacement. See
[Observation](/fhir/resources/observation#panel-classification).
# Code normalization
FHIR does not permit a code value to contain leading or trailing whitespace, or runs of internal whitespace. Because
source data occasionally carries such values, every code is normalized before publication:
1. Any run of whitespace inside the value is collapsed to a single space.
2. Leading and trailing whitespace is removed.
3. If nothing usable remains, the `code` element is omitted.
When `code` is omitted this way, the coding is still published with its `system` and `display`, so the clinical
description is not lost. This is done proactively so bundles remain valid FHIR rather than failing validation
downstream.