API reference

A FHIR R4 terminology API hosted in Scandinavia. One endpoint serves 28 code systems and 16 official cross-system mapping sets, scoped per tenant. The base URL is:

https://codon.theraponsystems.dk

1. Authentication

Every request carries a bearer API key. Keys are issued from the dashboard (Settings → API keys) and can be revoked at any time. The full token is shown exactly once on creation; the server stores only the prefix and a SHA-256 hash.

curl "https://codon.theraponsystems.dk/fhir/CodeSystem/$lookup?system=http://snomed.info/sct&code=73211009" \
  -H "Authorization: Bearer $NEXUS_API_KEY"

2. Code systems

28 code systems are loadable, including SNOMED CT (International + Danish extension), ICD-10 / ICD-11, SKS, LOINC, NPU, FSIII, ICPC-2 (NO), RxNorm, RadLex, ATC, OPS, HPO, Orphanet, CVX and UCUM. Identify a system by its canonical URL or OID — e.g. SNOMED CT http://snomed.info/sct, LOINC http://loinc.org, SKS urn:oid:1.2.208.176.2.4, NPU urn:oid:1.2.208.176.2.1.

3. Core operations

The terminology operations follow the FHIR R4 contract:

$lookup — resolve a code to its display + properties.
$validate-code — confirm a code is valid/current in a system or ValueSet.
$expand — expand a ValueSet (supports ECL 2.0 filters).
$subsumes — test the hierarchical relationship between two codes.
$translate / $chain-translate — map a code across systems (direct, or multi-hop through intermediary systems).
$closure — maintain an incremental transitive-closure table.

# Validate an ICD-10 code
curl "https://codon.theraponsystems.dk/fhir/CodeSystem/$validate-code?url=http://hl7.org/fhir/sid/icd-10&code=E11.9" \
  -H "Authorization: Bearer $NEXUS_API_KEY"

# Expand a ValueSet by canonical URL
curl "https://codon.theraponsystems.dk/fhir/ValueSet/$expand?url=https://nexus.theraponsystems.com/fhir/ValueSet/dk-diabetes-snomed" \
  -H "Authorization: Bearer $NEXUS_API_KEY"

4. ValueSets

Browse the shared ValueSets with GET /fhir/ValueSet and expand any of them via its canonical URL or id. ECL-defined ValueSets (e.g. << 73211009 |Diabetes mellitus|) expand against the loaded SNOMED CT edition.

5. Response format & errors

Responses are FHIR JSON (application/fhir+json). Errors return an OperationOutcome whose issue[].code follows the FHIR R4 IssueType:

Status	Meaning
400 / 422	Malformed, or well-formed but semantically invalid (e.g. unknown code)
401 / 403	Missing/invalid key, or the key lacks entitlement for the operation
404 / 410	Unknown resource, or a retired code
429	Monthly usage cap exceeded — body explains the cap + upgrade path

6. Rate limits & versioning

Usage is metered per tenant against a monthly plan budget; exceeding it returns 429. Pin a code-system version with the system-version parameter on $expand / $validate-code to lock against drift.

7. Data sovereignty

AI inference and terminology data never leave the host; the platform is hosted in Scandinavia. PHI features are a contracted add-on enabled under a data-processing agreement.

Need an example not covered here? Contact us or open an API key from the dashboard and try the operations above.