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Medical terminology system: ICD-10 (diagnosis), SNOMED CT (clinical), LOINC (laboratory), RxNorm (drug), CPT (procedure), ATC (drug classification). CodeSystem, ValueSet, ConceptMap in FHIR. Terminology binding (required, extensible, preferred, example). $validate-code, $expand, $lookup.

HL7 FHIR - Basic to Advanced Healthcare Data Standard

Part 4: Data Types, Terminologies and Profiles

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1. Main medical terminology systems

System	Organize	Purpose	FHIR system URI
ICD-10	WHO	Classification of diseases and causes of death	http://hl7.org/fhir/sid/icd-10
SNOMED CT	SNOMED Int'l	Comprehensive clinical terminology	http://snomed.info/sct
LOINC	Regenstrief	Laboratory testing and clinical observation	http://loinc.org
RxNorm	NLM	Standardized drug names (USA)	http://www.nlm.nih.gov/research/umls/rxnorm
ATC	WHO	Classification of drugs by group (international)	http://www.whocc.no/atc
CPT	AMA	Medical procedure/service code	http://www.ama-assn.org/go/cpt
CVX	CDC	Vaccine code	http://hl7.org/fhir/sid/cvx
UCUM	Regenstrief	Measurement unit	http://unitsofmeasure.org

ICD-10 — International Classification of Diseases

Use for Condition.code, Encounter.diagnosis. Vietnam uses the official ICD-10 (WHO).

{
  "system": "http://hl7.org/fhir/sid/icd-10",
  "code": "E11.9",
  "display": "Type 2 diabetes mellitus without complications"
}

SNOMED CT — Systematized Nomenclature of Medicine

The most comprehensive terminology system, 350,000+ concepts, hierarchical relationships (ontology).

{
  "system": "http://snomed.info/sct",
  "code": "73211009",
  "display": "Diabetes mellitus"
}

LOINC — Logical Observation Identifiers Names and Codes

97,000+ codes for testing and clinical observations. Used for Observation.code, DiagnosticReport.code.

{
  "system": "http://loinc.org",
  "code": "4548-4",
  "display": "Hemoglobin A1c/Hemoglobin.total in Blood"
}

2. CodeSystem Resource

CodeSystem defines a set of concepts (codes) — can be international or custom systems.

{
  "resourceType": "CodeSystem",
  "url": "http://hospital.vn/fhir/CodeSystem/loai-kham",
  "name": "LoaiKham",
  "title": "Loại hình khám chữa bệnh",
  "status": "active",
  "content": "complete",
  "count": 5,
  "concept": [
    {
      "code": "KSK",
      "display": "Khám sức khỏe",
      "definition": "Khám sức khỏe tổng quát định kỳ"
    },
    {
      "code": "KBT",
      "display": "Khám bệnh thường",
      "definition": "Khám bệnh ngoại trú thông thường"
    },
    {
      "code": "CC",
      "display": "Cấp cứu",
      "definition": "Khám cấp cứu"
    },
    {
      "code": "BHYT",
      "display": "Khám BHYT",
      "definition": "Khám bảo hiểm y tế"
    },
    {
      "code": "DV",
      "display": "Khám dịch vụ",
      "definition": "Khám theo yêu cầu (dịch vụ)"
    }
  ]
}

3. ValueSet Resource

ValueSet Select a subset from one or more CodeSystems.

{
  "resourceType": "ValueSet",
  "url": "http://hospital.vn/fhir/ValueSet/vital-signs-codes",
  "name": "VitalSignsCodes",
  "title": "Mã dấu hiệu sinh tồn",
  "status": "active",
  "compose": {
    "include": [
      {
        "system": "http://loinc.org",
        "concept": [
          {"code": "8480-6", "display": "Systolic blood pressure"},
          {"code": "8462-4", "display": "Diastolic blood pressure"},
          {"code": "8867-4", "display": "Heart rate"},
          {"code": "8310-5", "display": "Body temperature"},
          {"code": "9279-1", "display": "Respiratory rate"},
          {"code": "2708-6", "display": "Oxygen saturation (SpO2)"},
          {"code": "29463-7", "display": "Body weight"},
          {"code": "8302-2", "display": "Body height"}
        ]
      }
    ]
  }
}

ValueSet with Filter

{
  "resourceType": "ValueSet",
  "url": "http://hospital.vn/fhir/ValueSet/icd10-cardiovascular",
  "compose": {
    "include": [
      {
        "system": "http://hl7.org/fhir/sid/icd-10",
        "filter": [
          {
            "property": "concept",
            "op": "is-a",
            "value": "I00-I99"
          }
        ]
      }
    ],
    "exclude": [
      {
        "system": "http://hl7.org/fhir/sid/icd-10",
        "concept": [
          {"code": "I99"}
        ]
      }
    ]
  }
}

4. ConceptMap — Mapping between CodeSystems

{
  "resourceType": "ConceptMap",
  "url": "http://hospital.vn/fhir/ConceptMap/icd10-to-snomed",
  "name": "ICD10ToSNOMED",
  "title": "ICD-10 → SNOMED CT Mapping",
  "status": "active",
  "sourceScope": "http://hl7.org/fhir/sid/icd-10",
  "targetScope": "http://snomed.info/sct",
  "group": [
    {
      "source": "http://hl7.org/fhir/sid/icd-10",
      "target": "http://snomed.info/sct",
      "element": [
        {
          "code": "I10",
          "display": "Essential (primary) hypertension",
          "target": [
            {
              "code": "38341003",
              "display": "Hypertensive disorder",
              "relationship": "equivalent"
            }
          ]
        },
        {
          "code": "E11",
          "display": "Type 2 diabetes mellitus",
          "target": [
            {
              "code": "44054006",
              "display": "Type 2 diabetes mellitus",
              "relationship": "equivalent"
            }
          ]
        }
      ]
    }
  ]
}

Relationship Types

Relationship	Description
equivalent	Completely equivalent
source-is-narrower-than-target	Source is narrower than target
source-is-broader-than-target	Source is broader than target
not-related-to	Not related

5. Terminology Binding

Binding specifies which elements are REQUIRED to use codes from ValueSet.

Strength	Description	For example
required. required	REQUIRED to use code from ValueSet	Patient.gender
extensible	SHOULD be used. You can use another code if you cannot find it	Condition.code
preferred	RECOMMENDED. Other codes can be used	Encounter.type
example	Just examples. Any ValueSet can be used	Observation.code

6. Terminology Service Operations

# $validate-code — kiểm tra code có hợp lệ trong ValueSet
POST /ValueSet/$validate-code
{
  "resourceType": "Parameters",
  "parameter": [
    {"name": "url", "valueUri": "http://hl7.org/fhir/ValueSet/administrative-gender"},
    {"name": "code", "valueCode": "male"},
    {"name": "system", "valueUri": "http://hl7.org/fhir/administrative-gender"}
  ]
}

# $expand — mở rộng ValueSet ra danh sách codes
GET /ValueSet/$expand?url=http://hospital.vn/fhir/ValueSet/vital-signs-codes

# $lookup — tra cứu thông tin code
GET /CodeSystem/$lookup?system=http://loinc.org&code=4548-4

# $translate — ánh xạ code qua ConceptMap
GET /ConceptMap/$translate?system=http://hl7.org/fhir/sid/icd-10&code=I10&target=http://snomed.info/sct

7. Summary

CodeSystem — Define code sets (ICD-10, SNOMED CT, LOINC, or custom)
ValueSet — Select subset from CodeSystems, used for binding
ConceptMap — Mapping between CodeSystems (ICD-10 ↔ SNOMED CT)
Binding strengths — required > extensible > preferred > example
Terminology operations — $validate-code, $expand, $lookup, $translate

Lesson 12: Terminologies - CodeSystem, ValueSet, ConceptMap